Fairly minimal changes since the last set: tracefs is restricted at
Steven's suggestion (but could do with a once-over, I'm very much not a
vfs person), debugfs is back to Dave's original implementation. I've
also fixed up a malformed patch that resulted from me getting confused
during rebase, and added some further documentation to the initial patch
in order to give a reference for the design goals.
From: David Howells <[email protected]>
If the kernel is locked down, require that all modules have valid
signatures that we can verify.
I have adjusted the errors generated:
(1) If there's no signature (ENODATA) or we can't check it (ENOPKG,
ENOKEY), then:
(a) If signatures are enforced then EKEYREJECTED is returned.
(b) If there's no signature or we can't check it, but the kernel is
locked down then EPERM is returned (this is then consistent with
other lockdown cases).
(2) If the signature is unparseable (EBADMSG, EINVAL), the signature fails
the check (EKEYREJECTED) or a system error occurs (eg. ENOMEM), we
return the error we got.
Note that the X.509 code doesn't check for key expiry as the RTC might not
be valid or might not have been transferred to the kernel's clock yet.
[Modified by Matthew Garrett to remove the IMA integration. This will
be replaced with integration with the IMA architecture policy
patchset.]
Signed-off-by: David Howells <[email protected]>
Signed-off-by: Matthew Garrett <[email protected]>
Cc: Jessica Yu <[email protected]>
---
kernel/module.c | 39 ++++++++++++++++++++++++++++++++-------
1 file changed, 32 insertions(+), 7 deletions(-)
diff --git a/kernel/module.c b/kernel/module.c
index 2ad1b5239910..deea9d2763f8 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -2767,8 +2767,9 @@ static inline void kmemleak_load_module(const struct module *mod,
#ifdef CONFIG_MODULE_SIG
static int module_sig_check(struct load_info *info, int flags)
{
- int err = -ENOKEY;
+ int err = -ENODATA;
const unsigned long markerlen = sizeof(MODULE_SIG_STRING) - 1;
+ const char *reason;
const void *mod = info->hdr;
/*
@@ -2783,16 +2784,40 @@ static int module_sig_check(struct load_info *info, int flags)
err = mod_verify_sig(mod, info);
}
- if (!err) {
+ switch (err) {
+ case 0:
info->sig_ok = true;
return 0;
- }
- /* Not having a signature is only an error if we're strict. */
- if (err == -ENOKEY && !is_module_sig_enforced())
- err = 0;
+ /* We don't permit modules to be loaded into trusted kernels
+ * without a valid signature on them, but if we're not
+ * enforcing, certain errors are non-fatal.
+ */
+ case -ENODATA:
+ reason = "Loading of unsigned module";
+ goto decide;
+ case -ENOPKG:
+ reason = "Loading of module with unsupported crypto";
+ goto decide;
+ case -ENOKEY:
+ reason = "Loading of module with unavailable key";
+ decide:
+ if (is_module_sig_enforced()) {
+ pr_notice("%s is rejected\n", reason);
+ return -EKEYREJECTED;
+ }
- return err;
+ if (kernel_is_locked_down(reason, LOCKDOWN_INTEGRITY))
+ return -EPERM;
+ return 0;
+
+ /* All other errors are fatal, including nomem, unparseable
+ * signatures and signature check failures - even if signatures
+ * aren't required.
+ */
+ default:
+ return err;
+ }
}
#else /* !CONFIG_MODULE_SIG */
static int module_sig_check(struct load_info *info, int flags)
--
2.21.0.392.gf8f6787159e-goog
From: Matthew Garrett <[email protected]>
Allowing users to read and write to core kernel memory makes it possible
for the kernel to be subverted, avoiding module loading restrictions, and
also to steal cryptographic information.
Disallow /dev/mem and /dev/kmem from being opened this when the kernel has
been locked down to prevent this.
Also disallow /dev/port from being opened to prevent raw ioport access and
thus DMA from being used to accomplish the same thing.
Signed-off-by: David Howells <[email protected]>
Signed-off-by: Matthew Garrett <[email protected]>
Cc: [email protected]
---
drivers/char/mem.c | 2 ++
1 file changed, 2 insertions(+)
diff --git a/drivers/char/mem.c b/drivers/char/mem.c
index b08dc50f9f26..67b85939b1bd 100644
--- a/drivers/char/mem.c
+++ b/drivers/char/mem.c
@@ -786,6 +786,8 @@ static loff_t memory_lseek(struct file *file, loff_t offset, int orig)
static int open_port(struct inode *inode, struct file *filp)
{
+ if (kernel_is_locked_down("/dev/mem,kmem,port", LOCKDOWN_INTEGRITY))
+ return -EPERM;
return capable(CAP_SYS_RAWIO) ? 0 : -EPERM;
}
--
2.21.0.392.gf8f6787159e-goog
From: Jiri Bohac <[email protected]>
This is a preparatory patch for kexec_file_load() lockdown. A locked down
kernel needs to prevent unsigned kernel images from being loaded with
kexec_file_load(). Currently, the only way to force the signature
verification is compiling with KEXEC_VERIFY_SIG. This prevents loading
usigned images even when the kernel is not locked down at runtime.
This patch splits KEXEC_VERIFY_SIG into KEXEC_SIG and KEXEC_SIG_FORCE.
Analogous to the MODULE_SIG and MODULE_SIG_FORCE for modules, KEXEC_SIG
turns on the signature verification but allows unsigned images to be
loaded. KEXEC_SIG_FORCE disallows images without a valid signature.
[Modified by David Howells such that:
(1) verify_pefile_signature() differentiates between no-signature and
sig-didn't-match in its returned errors.
(2) kexec fails with EKEYREJECTED and logs an appropriate message if
signature checking is enforced and an signature is not found, uses
unsupported crypto or has no matching key.
(3) kexec fails with EKEYREJECTED if there is a signature for which we
have a key, but signature doesn't match - even if in non-forcing mode.
(4) kexec fails with EBADMSG or some other error if there is a signature
which cannot be parsed - even if in non-forcing mode.
(5) kexec fails with ELIBBAD if the PE file cannot be parsed to extract
the signature - even if in non-forcing mode.
]
Signed-off-by: Jiri Bohac <[email protected]>
Signed-off-by: David Howells <[email protected]>
Signed-off-by: Matthew Garrett <[email protected]>
Reviewed-by: Jiri Bohac <[email protected]>
cc: [email protected]
---
arch/x86/Kconfig | 20 ++++++++---
crypto/asymmetric_keys/verify_pefile.c | 4 ++-
include/linux/kexec.h | 4 +--
kernel/kexec_file.c | 48 ++++++++++++++++++++++----
4 files changed, 61 insertions(+), 15 deletions(-)
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 4b4a7f32b68e..735d04a4b18f 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -2016,20 +2016,30 @@ config KEXEC_FILE
config ARCH_HAS_KEXEC_PURGATORY
def_bool KEXEC_FILE
-config KEXEC_VERIFY_SIG
+config KEXEC_SIG
bool "Verify kernel signature during kexec_file_load() syscall"
depends on KEXEC_FILE
---help---
- This option makes kernel signature verification mandatory for
- the kexec_file_load() syscall.
- In addition to that option, you need to enable signature
+ This option makes the kexec_file_load() syscall check for a valid
+ signature of the kernel image. The image can still be loaded without
+ a valid signature unless you also enable KEXEC_SIG_FORCE, though if
+ there's a signature that we can check, then it must be valid.
+
+ In addition to this option, you need to enable signature
verification for the corresponding kernel image type being
loaded in order for this to work.
+config KEXEC_SIG_FORCE
+ bool "Require a valid signature in kexec_file_load() syscall"
+ depends on KEXEC_SIG
+ ---help---
+ This option makes kernel signature verification mandatory for
+ the kexec_file_load() syscall.
+
config KEXEC_BZIMAGE_VERIFY_SIG
bool "Enable bzImage signature verification support"
- depends on KEXEC_VERIFY_SIG
+ depends on KEXEC_SIG
depends on SIGNED_PE_FILE_VERIFICATION
select SYSTEM_TRUSTED_KEYRING
---help---
diff --git a/crypto/asymmetric_keys/verify_pefile.c b/crypto/asymmetric_keys/verify_pefile.c
index d178650fd524..4473cea1e877 100644
--- a/crypto/asymmetric_keys/verify_pefile.c
+++ b/crypto/asymmetric_keys/verify_pefile.c
@@ -100,7 +100,7 @@ static int pefile_parse_binary(const void *pebuf, unsigned int pelen,
if (!ddir->certs.virtual_address || !ddir->certs.size) {
pr_debug("Unsigned PE binary\n");
- return -EKEYREJECTED;
+ return -ENODATA;
}
chkaddr(ctx->header_size, ddir->certs.virtual_address,
@@ -408,6 +408,8 @@ static int pefile_digest_pe(const void *pebuf, unsigned int pelen,
* (*) 0 if at least one signature chain intersects with the keys in the trust
* keyring, or:
*
+ * (*) -ENODATA if there is no signature present.
+ *
* (*) -ENOPKG if a suitable crypto module couldn't be found for a check on a
* chain.
*
diff --git a/include/linux/kexec.h b/include/linux/kexec.h
index b9b1bc5f9669..58b27c7bdc2b 100644
--- a/include/linux/kexec.h
+++ b/include/linux/kexec.h
@@ -125,7 +125,7 @@ typedef void *(kexec_load_t)(struct kimage *image, char *kernel_buf,
unsigned long cmdline_len);
typedef int (kexec_cleanup_t)(void *loader_data);
-#ifdef CONFIG_KEXEC_VERIFY_SIG
+#ifdef CONFIG_KEXEC_SIG
typedef int (kexec_verify_sig_t)(const char *kernel_buf,
unsigned long kernel_len);
#endif
@@ -134,7 +134,7 @@ struct kexec_file_ops {
kexec_probe_t *probe;
kexec_load_t *load;
kexec_cleanup_t *cleanup;
-#ifdef CONFIG_KEXEC_VERIFY_SIG
+#ifdef CONFIG_KEXEC_SIG
kexec_verify_sig_t *verify_sig;
#endif
};
diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c
index f1d0e00a3971..67f3a866eabe 100644
--- a/kernel/kexec_file.c
+++ b/kernel/kexec_file.c
@@ -90,7 +90,7 @@ int __weak arch_kimage_file_post_load_cleanup(struct kimage *image)
return kexec_image_post_load_cleanup_default(image);
}
-#ifdef CONFIG_KEXEC_VERIFY_SIG
+#ifdef CONFIG_KEXEC_SIG
static int kexec_image_verify_sig_default(struct kimage *image, void *buf,
unsigned long buf_len)
{
@@ -188,7 +188,8 @@ kimage_file_prepare_segments(struct kimage *image, int kernel_fd, int initrd_fd,
const char __user *cmdline_ptr,
unsigned long cmdline_len, unsigned flags)
{
- int ret = 0;
+ const char *reason;
+ int ret;
void *ldata;
loff_t size;
@@ -207,15 +208,48 @@ kimage_file_prepare_segments(struct kimage *image, int kernel_fd, int initrd_fd,
if (ret)
goto out;
-#ifdef CONFIG_KEXEC_VERIFY_SIG
+#ifdef CONFIG_KEXEC_SIG
ret = arch_kexec_kernel_verify_sig(image, image->kernel_buf,
image->kernel_buf_len);
- if (ret) {
- pr_debug("kernel signature verification failed.\n");
+#else
+ ret = -ENODATA;
+#endif
+
+ switch (ret) {
+ case 0:
+ break;
+
+ /* Certain verification errors are non-fatal if we're not
+ * checking errors, provided we aren't mandating that there
+ * must be a valid signature.
+ */
+ case -ENODATA:
+ reason = "kexec of unsigned image";
+ goto decide;
+ case -ENOPKG:
+ reason = "kexec of image with unsupported crypto";
+ goto decide;
+ case -ENOKEY:
+ reason = "kexec of image with unavailable key";
+ decide:
+ if (IS_ENABLED(CONFIG_KEXEC_SIG_FORCE)) {
+ pr_notice("%s rejected\n", reason);
+ ret = -EKEYREJECTED;
+ goto out;
+ }
+
+ ret = 0;
+ break;
+
+ /* All other errors are fatal, including nomem, unparseable
+ * signatures and signature check failures - even if signatures
+ * aren't required.
+ */
+ default:
+ pr_notice("kernel signature verification failed (%d).\n", ret);
goto out;
}
- pr_debug("kernel signature verification successful.\n");
-#endif
+
/* It is possible that there no initramfs is being loaded */
if (!(flags & KEXEC_FILE_NO_INITRAMFS)) {
ret = kernel_read_file_from_fd(initrd_fd, &image->initrd_buf,
--
2.21.0.392.gf8f6787159e-goog
From: Josh Boyer <[email protected]>
There is currently no way to verify the resume image when returning
from hibernate. This might compromise the signed modules trust model,
so until we can work with signed hibernate images we disable it when the
kernel is locked down.
Signed-off-by: Josh Boyer <[email protected]>
Signed-off-by: David Howells <[email protected]>
Signed-off-by: Matthew Garrett <[email protected]>
Cc: [email protected]
Cc: [email protected]
cc: [email protected]
---
kernel/power/hibernate.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/kernel/power/hibernate.c b/kernel/power/hibernate.c
index abef759de7c8..928b198cfa26 100644
--- a/kernel/power/hibernate.c
+++ b/kernel/power/hibernate.c
@@ -70,7 +70,8 @@ static const struct platform_hibernation_ops *hibernation_ops;
bool hibernation_available(void)
{
- return (nohibernate == 0);
+ return nohibernate == 0 && !kernel_is_locked_down("Hibernation",
+ LOCKDOWN_INTEGRITY);
}
/**
--
2.21.0.392.gf8f6787159e-goog
From: Matthew Garrett <[email protected]>
Any hardware that can potentially generate DMA has to be locked down in
order to avoid it being possible for an attacker to modify kernel code,
allowing them to circumvent disabled module loading or module signing.
Default to paranoid - in future we can potentially relax this for
sufficiently IOMMU-isolated devices.
Signed-off-by: David Howells <[email protected]>
Signed-off-by: Matthew Garrett <[email protected]>
Acked-by: Bjorn Helgaas <[email protected]>
cc: [email protected]
---
drivers/pci/pci-sysfs.c | 9 +++++++++
drivers/pci/proc.c | 9 ++++++++-
drivers/pci/syscall.c | 3 ++-
3 files changed, 19 insertions(+), 2 deletions(-)
diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c
index 9ecfe13157c0..59d02088945e 100644
--- a/drivers/pci/pci-sysfs.c
+++ b/drivers/pci/pci-sysfs.c
@@ -905,6 +905,9 @@ static ssize_t pci_write_config(struct file *filp, struct kobject *kobj,
loff_t init_off = off;
u8 *data = (u8 *) buf;
+ if (kernel_is_locked_down("Direct PCI access", LOCKDOWN_INTEGRITY))
+ return -EPERM;
+
if (off > dev->cfg_size)
return 0;
if (off + count > dev->cfg_size) {
@@ -1167,6 +1170,9 @@ static int pci_mmap_resource(struct kobject *kobj, struct bin_attribute *attr,
enum pci_mmap_state mmap_type;
struct resource *res = &pdev->resource[bar];
+ if (kernel_is_locked_down("Direct PCI access", LOCKDOWN_INTEGRITY))
+ return -EPERM;
+
if (res->flags & IORESOURCE_MEM && iomem_is_exclusive(res->start))
return -EINVAL;
@@ -1242,6 +1248,9 @@ static ssize_t pci_write_resource_io(struct file *filp, struct kobject *kobj,
struct bin_attribute *attr, char *buf,
loff_t off, size_t count)
{
+ if (kernel_is_locked_down("Direct PCI access", LOCKDOWN_INTEGRITY))
+ return -EPERM;
+
return pci_resource_io(filp, kobj, attr, buf, off, count, true);
}
diff --git a/drivers/pci/proc.c b/drivers/pci/proc.c
index 6fa1627ce08d..85769f222b6d 100644
--- a/drivers/pci/proc.c
+++ b/drivers/pci/proc.c
@@ -117,6 +117,9 @@ static ssize_t proc_bus_pci_write(struct file *file, const char __user *buf,
int size = dev->cfg_size;
int cnt;
+ if (kernel_is_locked_down("Direct PCI access", LOCKDOWN_INTEGRITY))
+ return -EPERM;
+
if (pos >= size)
return 0;
if (nbytes >= size)
@@ -196,6 +199,9 @@ static long proc_bus_pci_ioctl(struct file *file, unsigned int cmd,
#endif /* HAVE_PCI_MMAP */
int ret = 0;
+ if (kernel_is_locked_down("Direct PCI access", LOCKDOWN_INTEGRITY))
+ return -EPERM;
+
switch (cmd) {
case PCIIOC_CONTROLLER:
ret = pci_domain_nr(dev->bus);
@@ -237,7 +243,8 @@ static int proc_bus_pci_mmap(struct file *file, struct vm_area_struct *vma)
struct pci_filp_private *fpriv = file->private_data;
int i, ret, write_combine = 0, res_bit = IORESOURCE_MEM;
- if (!capable(CAP_SYS_RAWIO))
+ if (!capable(CAP_SYS_RAWIO) ||
+ kernel_is_locked_down("Direct PCI access", LOCKDOWN_INTEGRITY))
return -EPERM;
if (fpriv->mmap_state == pci_mmap_io) {
diff --git a/drivers/pci/syscall.c b/drivers/pci/syscall.c
index d96626c614f5..0669cb09e792 100644
--- a/drivers/pci/syscall.c
+++ b/drivers/pci/syscall.c
@@ -90,7 +90,8 @@ SYSCALL_DEFINE5(pciconfig_write, unsigned long, bus, unsigned long, dfn,
u32 dword;
int err = 0;
- if (!capable(CAP_SYS_ADMIN))
+ if (!capable(CAP_SYS_ADMIN) ||
+ kernel_is_locked_down("Direct PCI access", LOCKDOWN_INTEGRITY))
return -EPERM;
dev = pci_get_domain_bus_and_slot(0, bus, dfn);
--
2.21.0.392.gf8f6787159e-goog
From: Matthew Garrett <[email protected]>
IO port access would permit users to gain access to PCI configuration
registers, which in turn (on a lot of hardware) give access to MMIO
register space. This would potentially permit root to trigger arbitrary
DMA, so lock it down by default.
This also implicitly locks down the KDADDIO, KDDELIO, KDENABIO and
KDDISABIO console ioctls.
Signed-off-by: Matthew Garrett <[email protected]>
Signed-off-by: David Howells <[email protected]>
cc: [email protected]
---
arch/x86/kernel/ioport.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)
diff --git a/arch/x86/kernel/ioport.c b/arch/x86/kernel/ioport.c
index 0fe1c8782208..febbd7eb847c 100644
--- a/arch/x86/kernel/ioport.c
+++ b/arch/x86/kernel/ioport.c
@@ -31,7 +31,8 @@ long ksys_ioperm(unsigned long from, unsigned long num, int turn_on)
if ((from + num <= from) || (from + num > IO_BITMAP_BITS))
return -EINVAL;
- if (turn_on && !capable(CAP_SYS_RAWIO))
+ if (turn_on && (!capable(CAP_SYS_RAWIO) ||
+ kernel_is_locked_down("ioperm", LOCKDOWN_INTEGRITY)))
return -EPERM;
/*
@@ -126,7 +127,8 @@ SYSCALL_DEFINE1(iopl, unsigned int, level)
return -EINVAL;
/* Trying to gain more privileges? */
if (level > old) {
- if (!capable(CAP_SYS_RAWIO))
+ if (!capable(CAP_SYS_RAWIO) ||
+ kernel_is_locked_down("iopl", LOCKDOWN_INTEGRITY))
return -EPERM;
}
regs->flags = (regs->flags & ~X86_EFLAGS_IOPL) |
--
2.21.0.392.gf8f6787159e-goog
From: Matthew Garrett <[email protected]>
Writing to MSRs should not be allowed if the kernel is locked down, since
it could lead to execution of arbitrary code in kernel mode. Based on a
patch by Kees Cook.
Signed-off-by: Matthew Garrett <[email protected]>
Signed-off-by: David Howells <[email protected]>
Acked-by: Kees Cook <[email protected]>
Reviewed-by: Thomas Gleixner <[email protected]>
cc: [email protected]
---
arch/x86/kernel/msr.c | 8 ++++++++
1 file changed, 8 insertions(+)
diff --git a/arch/x86/kernel/msr.c b/arch/x86/kernel/msr.c
index 4588414e2561..731be1be52b6 100644
--- a/arch/x86/kernel/msr.c
+++ b/arch/x86/kernel/msr.c
@@ -84,6 +84,9 @@ static ssize_t msr_write(struct file *file, const char __user *buf,
int err = 0;
ssize_t bytes = 0;
+ if (kernel_is_locked_down("Direct MSR access", LOCKDOWN_INTEGRITY))
+ return -EPERM;
+
if (count % 8)
return -EINVAL; /* Invalid chunk size */
@@ -135,6 +138,11 @@ static long msr_ioctl(struct file *file, unsigned int ioc, unsigned long arg)
err = -EFAULT;
break;
}
+ if (kernel_is_locked_down("Direct MSR access",
+ LOCKDOWN_INTEGRITY)) {
+ err = -EPERM;
+ break;
+ }
err = wrmsr_safe_regs_on_cpu(cpu, regs);
if (err)
break;
--
2.21.0.392.gf8f6787159e-goog
From: Linn Crosetto <[email protected]>
From the kernel documentation (initrd_table_override.txt):
If the ACPI_INITRD_TABLE_OVERRIDE compile option is true, it is possible
to override nearly any ACPI table provided by the BIOS with an
instrumented, modified one.
When lockdown is enabled, the kernel should disallow any unauthenticated
changes to kernel space. ACPI tables contain code invoked by the kernel,
so do not allow ACPI tables to be overridden if the kernel is locked down.
Signed-off-by: Linn Crosetto <[email protected]>
Signed-off-by: David Howells <[email protected]>
Signed-off-by: Matthew Garrett <[email protected]>
cc: [email protected]
---
drivers/acpi/tables.c | 5 +++++
1 file changed, 5 insertions(+)
diff --git a/drivers/acpi/tables.c b/drivers/acpi/tables.c
index 48eabb6c2d4f..0dc561210c86 100644
--- a/drivers/acpi/tables.c
+++ b/drivers/acpi/tables.c
@@ -531,6 +531,11 @@ void __init acpi_table_upgrade(void)
if (table_nr == 0)
return;
+ if (kernel_is_locked_down("ACPI table override", LOCKDOWN_INTEGRITY)) {
+ pr_notice("kernel is locked down, ignoring table override\n");
+ return;
+ }
+
acpi_tables_addr =
memblock_find_in_range(0, ACPI_TABLE_UPGRADE_MAX_PHYS,
all_tables_size, PAGE_SIZE);
--
2.21.0.392.gf8f6787159e-goog
From: David Howells <[email protected]>
Prohibit replacement of the PCMCIA Card Information Structure when the
kernel is locked down.
Suggested-by: Dominik Brodowski <[email protected]>
Signed-off-by: David Howells <[email protected]>
Signed-off-by: Matthew Garrett <[email protected]>
---
drivers/pcmcia/cistpl.c | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/drivers/pcmcia/cistpl.c b/drivers/pcmcia/cistpl.c
index ac0672b8dfca..9e23300a55e5 100644
--- a/drivers/pcmcia/cistpl.c
+++ b/drivers/pcmcia/cistpl.c
@@ -1578,6 +1578,10 @@ static ssize_t pccard_store_cis(struct file *filp, struct kobject *kobj,
struct pcmcia_socket *s;
int error;
+ if (kernel_is_locked_down("Direct PCMCIA CIS storage",
+ LOCKDOWN_INTEGRITY))
+ return -EPERM;
+
s = to_socket(container_of(kobj, struct device, kobj));
if (off)
--
2.21.0.392.gf8f6787159e-goog
From: David Howells <[email protected]>
Disallow access to /proc/kcore when the kernel is locked down to prevent
access to cryptographic data. This is limited to lockdown
confidentiality mode and is still permitted in integrity mode.
Signed-off-by: David Howells <[email protected]>
Signed-off-by: Matthew Garrett <[email protected]>
---
fs/proc/kcore.c | 2 ++
1 file changed, 2 insertions(+)
diff --git a/fs/proc/kcore.c b/fs/proc/kcore.c
index bbcc185062bb..1c556a453569 100644
--- a/fs/proc/kcore.c
+++ b/fs/proc/kcore.c
@@ -518,6 +518,8 @@ read_kcore(struct file *file, char __user *buffer, size_t buflen, loff_t *fpos)
static int open_kcore(struct inode *inode, struct file *filp)
{
+ if (kernel_is_locked_down("/proc/kcore", LOCKDOWN_CONFIDENTIALITY))
+ return -EPERM;
if (!capable(CAP_SYS_RAWIO))
return -EPERM;
--
2.21.0.392.gf8f6787159e-goog
From: David Howells <[email protected]>
Provide a single call to allow kernel code to determine whether the system
should be locked down, thereby disallowing various accesses that might
allow the running kernel image to be changed including the loading of
modules that aren't validly signed with a key we recognise, fiddling with
MSR registers and disallowing hibernation.
Signed-off-by: David Howells <[email protected]>
Signed-off-by: Matthew Garrett <[email protected]>
---
Documentation/ABI/testing/lockdown | 19 +++
.../admin-guide/kernel-parameters.txt | 9 ++
Documentation/admin-guide/lockdown.rst | 60 +++++++
include/linux/kernel.h | 28 ++++
include/linux/security.h | 9 +-
init/main.c | 1 +
security/Kconfig | 39 +++++
security/Makefile | 3 +
security/lock_down.c | 147 ++++++++++++++++++
9 files changed, 314 insertions(+), 1 deletion(-)
create mode 100644 Documentation/ABI/testing/lockdown
create mode 100644 Documentation/admin-guide/lockdown.rst
create mode 100644 security/lock_down.c
diff --git a/Documentation/ABI/testing/lockdown b/Documentation/ABI/testing/lockdown
new file mode 100644
index 000000000000..5bd51e20917a
--- /dev/null
+++ b/Documentation/ABI/testing/lockdown
@@ -0,0 +1,19 @@
+What: security/lockdown
+Date: March 2019
+Contact: Matthew Garrett <[email protected]>
+Description:
+ If CONFIG_LOCK_DOWN_KERNEL is enabled, the kernel can be
+ moved to a more locked down state at runtime by writing to
+ this attribute. Valid values are:
+
+ integrity:
+ The kernel will disable functionality that allows
+ userland to modify the running kernel image, other
+ than through the loading or execution of appropriately
+ signed objects.
+
+ confidentiality:
+ The kernel will disable all functionality disabled by
+ the integrity mode, but additionally will disable
+ features that potentially permit userland to obtain
+ confidential information stored within the kernel.
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 91c0251fdb86..594d268d92ba 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -2213,6 +2213,15 @@
lockd.nlm_udpport=M [NFS] Assign UDP port.
Format: <integer>
+ lockdown= [SECURITY]
+ { integrity | confidentiality }
+ Enable the kernel lockdown feature. If set to
+ integrity, kernel features that allow userland to
+ modify the running kernel are disabled. If set to
+ confidentiality, kernel features that allow userland
+ to extract confidential information from the kernel
+ are also disabled.
+
locktorture.nreaders_stress= [KNL]
Set the number of locking read-acquisition kthreads.
Defaults to being automatically set based on the
diff --git a/Documentation/admin-guide/lockdown.rst b/Documentation/admin-guide/lockdown.rst
new file mode 100644
index 000000000000..d05dcedd20d1
--- /dev/null
+++ b/Documentation/admin-guide/lockdown.rst
@@ -0,0 +1,60 @@
+Kernel lockdown functionality
+-----------------------------
+
+.. CONTENTS
+..
+.. - Overview.
+.. - Enabling Lockdown.
+
+========
+Overview
+========
+
+Traditionally Linux systems have been run with the presumption that a
+process running with full capabilities is effectively equivalent in
+privilege to the kernel itself. The lockdown feature attempts to draw
+a stronger boundary between privileged processes and the kernel,
+increasing the level of trust that can be placed in the kernel even in
+the face of hostile processes.
+
+Lockdown can be run in two modes - integrity and confidentiality. In
+integrity mode, kernel features that allow arbitrary modification of
+the running kernel image are disabled. Confidentiality mode behaves in
+the same way as integrity mode, but also blocks features that
+potentially allow a hostile userland process to extract secret
+information from the kernel.
+
+Note that lockdown depends upon the correct behaviour of the
+kernel. Exploitable vulnerabilities in the kernel may still permit
+arbitrary modification of the kernel or make it possible to disable
+lockdown features.
+
+=================
+Enabling Lockdown
+=================
+
+Lockdown can be enabled in multiple ways.
+
+Kernel configuration
+====================
+
+The kernel can be statically configured by setting either
+CONFIG_LOCK_DOWN_KERNEL_FORCE_INTEGRITY or
+CONFIG_LOCK_DOWN_KERNEL_FORCE_CONFIDENTIALITY. A kernel configured
+with CONFIG_LOCK_DOWN_KERNEL_FORCE_INTEGRITY may be booted into
+confidentiality mode using one of the other mechanisms, but otherwise
+the kernel will always boot into the configured mode.
+
+Kernel command line
+===================
+
+Passing lockdown=integrity or lockdown=confidentiality on the kernel
+command line will configure lockdown into the appropriate mode.
+
+Runtime configuration
+=====================
+
+/sys/kernel/security/lockdown will indicate the current lockdown
+state. The system state may be made stricter by writing either
+"integrity" or "confidentiality" into this file, but any attempts to
+make it less strict will fail.
diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index 8f0e68e250a7..30cf695719d5 100644
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -340,6 +340,34 @@ static inline void refcount_error_report(struct pt_regs *regs, const char *err)
{ }
#endif
+enum lockdown_level {
+ LOCKDOWN_NONE,
+ LOCKDOWN_INTEGRITY,
+ LOCKDOWN_CONFIDENTIALITY,
+ LOCKDOWN_MAX,
+};
+
+#ifdef CONFIG_LOCK_DOWN_KERNEL
+extern bool __kernel_is_locked_down(const char *what,
+ enum lockdown_level level,
+ bool first);
+#else
+static inline bool __kernel_is_locked_down(const char *what,
+ enum lockdown_level level,
+ bool first)
+{
+ return false;
+}
+#endif
+
+#define kernel_is_locked_down(what, level) \
+ ({ \
+ static bool message_given; \
+ bool locked_down = __kernel_is_locked_down(what, level, !message_given); \
+ message_given = true; \
+ locked_down; \
+ })
+
/* Internal, do not use. */
int __must_check _kstrtoul(const char *s, unsigned int base, unsigned long *res);
int __must_check _kstrtol(const char *s, unsigned int base, long *res);
diff --git a/include/linux/security.h b/include/linux/security.h
index 13537a49ae97..b290946341a4 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -1798,5 +1798,12 @@ static inline void security_bpf_prog_free(struct bpf_prog_aux *aux)
#endif /* CONFIG_SECURITY */
#endif /* CONFIG_BPF_SYSCALL */
-#endif /* ! __LINUX_SECURITY_H */
+#ifdef CONFIG_LOCK_DOWN_KERNEL
+extern void __init init_lockdown(void);
+#else
+static inline void __init init_lockdown(void)
+{
+}
+#endif
+#endif /* ! __LINUX_SECURITY_H */
diff --git a/init/main.c b/init/main.c
index e2e80ca3165a..4c6cca9681c7 100644
--- a/init/main.c
+++ b/init/main.c
@@ -555,6 +555,7 @@ asmlinkage __visible void __init start_kernel(void)
boot_cpu_init();
page_address_init();
pr_notice("%s", linux_banner);
+ init_lockdown();
setup_arch(&command_line);
/*
* Set up the the initial canary and entropy after arch
diff --git a/security/Kconfig b/security/Kconfig
index 1d6463fb1450..593ff231eac6 100644
--- a/security/Kconfig
+++ b/security/Kconfig
@@ -229,6 +229,45 @@ config STATIC_USERMODEHELPER_PATH
If you wish for all usermode helper programs to be disabled,
specify an empty string here (i.e. "").
+config LOCK_DOWN_KERNEL
+ bool "Allow the kernel to be 'locked down'"
+ help
+ Allow the kernel to be locked down. If lockdown support is enabled
+ and activated, the kernel will impose additional restrictions
+ intended to prevent uid 0 from being able to modify the running
+ kernel. This may break userland applications that rely on low-level
+ access to hardware.
+
+choice
+ prompt "Kernel default lockdown mode"
+ default LOCK_DOWN_KERNEL_FORCE_NONE
+ depends on LOCK_DOWN_KERNEL
+ help
+ The kernel can be configured to default to differing levels of
+ lockdown.
+
+config LOCK_DOWN_KERNEL_FORCE_NONE
+ bool "None"
+ help
+ No lockdown functionality is enabled by default. Lockdown may be
+ enabled via the kernel commandline or /sys/kernel/security/lockdown.
+
+config LOCK_DOWN_KERNEL_FORCE_INTEGRITY
+ bool "Integrity"
+ help
+ The kernel runs in integrity mode by default. Features that allow
+ the kernel to be modified at runtime are disabled.
+
+config LOCK_DOWN_KERNEL_FORCE_CONFIDENTIALITY
+ bool "Confidentiality"
+ help
+ The kernel runs in confidentiality mode by default. Features that
+ allow the kernel to be modified at runtime or that permit userland
+ code to read confidential material held inside the kernel are
+ disabled.
+
+endchoice
+
source "security/selinux/Kconfig"
source "security/smack/Kconfig"
source "security/tomoyo/Kconfig"
diff --git a/security/Makefile b/security/Makefile
index c598b904938f..5ff090149c88 100644
--- a/security/Makefile
+++ b/security/Makefile
@@ -32,3 +32,6 @@ obj-$(CONFIG_CGROUP_DEVICE) += device_cgroup.o
# Object integrity file lists
subdir-$(CONFIG_INTEGRITY) += integrity
obj-$(CONFIG_INTEGRITY) += integrity/
+
+# Allow the kernel to be locked down
+obj-$(CONFIG_LOCK_DOWN_KERNEL) += lock_down.o
diff --git a/security/lock_down.c b/security/lock_down.c
new file mode 100644
index 000000000000..9913fff09ad0
--- /dev/null
+++ b/security/lock_down.c
@@ -0,0 +1,147 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Lock down the kernel
+ *
+ * Copyright (C) 2016 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells ([email protected])
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public Licence
+ * as published by the Free Software Foundation; either version
+ * 2 of the Licence, or (at your option) any later version.
+ */
+
+#include <linux/security.h>
+#include <linux/export.h>
+
+static enum lockdown_level kernel_locked_down;
+
+char *lockdown_levels[LOCKDOWN_MAX] = {"none", "integrity", "confidentiality"};
+
+/*
+ * Put the kernel into lock-down mode.
+ */
+static int lock_kernel_down(const char *where, enum lockdown_level level)
+{
+ if (kernel_locked_down >= level)
+ return -EPERM;
+
+ kernel_locked_down = level;
+ pr_notice("Kernel is locked down from %s; see man kernel_lockdown.7\n",
+ where);
+ return 0;
+}
+
+static int __init lockdown_param(char *level)
+{
+ if (!level)
+ return -EINVAL;
+
+ if (strcmp(level, "integrity") == 0)
+ lock_kernel_down("command line", LOCKDOWN_INTEGRITY);
+ else if (strcmp(level, "confidentiality") == 0)
+ lock_kernel_down("command line", LOCKDOWN_CONFIDENTIALITY);
+ else
+ return -EINVAL;
+
+ return 0;
+}
+
+early_param("lockdown", lockdown_param);
+
+/*
+ * This must be called before arch setup code in order to ensure that the
+ * appropriate default can be applied without being overridden by the command
+ * line option.
+ */
+void __init init_lockdown(void)
+{
+#if defined(CONFIG_LOCK_DOWN_KERNEL_FORCE_INTEGRITY)
+ lock_kernel_down("Kernel configuration", LOCKDOWN_INTEGRITY);
+#elif defined(CONFIG_LOCK_DOWN_KERNEL_FORCE_CONFIDENTIALITY)
+ lock_kernel_down("Kernel configuration", LOCKDOWN_CONFIDENTIALITY);
+#endif
+}
+
+/**
+ * kernel_is_locked_down - Find out if the kernel is locked down
+ * @what: Tag to use in notice generated if lockdown is in effect
+ */
+bool __kernel_is_locked_down(const char *what, enum lockdown_level level,
+ bool first)
+{
+ if ((kernel_locked_down >= level) && what && first)
+ pr_notice("Lockdown: %s is restricted; see man kernel_lockdown.7\n",
+ what);
+ return (kernel_locked_down >= level);
+}
+EXPORT_SYMBOL(__kernel_is_locked_down);
+
+static ssize_t lockdown_read(struct file *filp, char __user *buf, size_t count,
+ loff_t *ppos)
+{
+ char temp[80];
+ int i, offset=0;
+
+ for (i = LOCKDOWN_NONE; i < LOCKDOWN_MAX; i++) {
+ if (lockdown_levels[i]) {
+ const char *label = lockdown_levels[i];
+
+ if (kernel_locked_down == i)
+ offset += sprintf(temp+offset, "[%s] ", label);
+ else
+ offset += sprintf(temp+offset, "%s ", label);
+ }
+ }
+
+ /* Convert the last space to a newline if needed. */
+ if (offset > 0)
+ temp[offset-1] = '\n';
+
+ return simple_read_from_buffer(buf, count, ppos, temp, strlen(temp));
+}
+
+static ssize_t lockdown_write(struct file *file, const char __user *buf,
+ size_t n, loff_t *ppos)
+{
+ char *state;
+ int i, len, err = -EINVAL;
+
+ state = memdup_user_nul(buf, n);
+ if (IS_ERR(state))
+ return PTR_ERR(state);
+
+ len = strlen(state);
+ if (len && state[len-1] == '\n') {
+ state[len-1] = '\0';
+ len--;
+ }
+
+ for (i = 0; i < LOCKDOWN_MAX; i++) {
+ const char *label = lockdown_levels[i];
+
+ if (label && !strcmp(state, label))
+ err = lock_kernel_down("securityfs", i);
+ }
+
+ kfree(state);
+ return err ? err : n;
+}
+
+static const struct file_operations lockdown_ops = {
+ .read = lockdown_read,
+ .write = lockdown_write,
+};
+
+static int __init lockdown_secfs_init(void)
+{
+ struct dentry *dentry;
+
+ dentry = securityfs_create_file("lockdown", 0600, NULL, NULL,
+ &lockdown_ops);
+ if (IS_ERR(dentry))
+ return PTR_ERR(dentry);
+
+ return 0;
+}
+
+core_initcall(lockdown_secfs_init);
--
2.21.0.392.gf8f6787159e-goog
From: David Howells <[email protected]>
There are some bpf functions can be used to read kernel memory:
bpf_probe_read, bpf_probe_write_user and bpf_trace_printk. These allow
private keys in kernel memory (e.g. the hibernation image signing key) to
be read by an eBPF program and kernel memory to be altered without
restriction. Disable them if the kernel has been locked down in
confidentiality mode.
Suggested-by: Alexei Starovoitov <[email protected]>
Signed-off-by: David Howells <[email protected]>
Signed-off-by: Matthew Garrett <[email protected]>
cc: [email protected]
cc: Chun-Yi Lee <[email protected]>
cc: Alexei Starovoitov <[email protected]>
Cc: Daniel Borkmann <[email protected]>
---
kernel/trace/bpf_trace.c | 11 +++++++++++
1 file changed, 11 insertions(+)
diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index 8b068adb9da1..9e8eda605b5e 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -137,6 +137,9 @@ BPF_CALL_3(bpf_probe_read, void *, dst, u32, size, const void *, unsafe_ptr)
{
int ret;
+ if (kernel_is_locked_down("BPF", LOCKDOWN_CONFIDENTIALITY))
+ return -EINVAL;
+
ret = probe_kernel_read(dst, unsafe_ptr, size);
if (unlikely(ret < 0))
memset(dst, 0, size);
@@ -156,6 +159,8 @@ static const struct bpf_func_proto bpf_probe_read_proto = {
BPF_CALL_3(bpf_probe_write_user, void *, unsafe_ptr, const void *, src,
u32, size)
{
+ if (kernel_is_locked_down("BPF", LOCKDOWN_CONFIDENTIALITY))
+ return -EINVAL;
/*
* Ensure we're in user context which is safe for the helper to
* run. This helper has no business in a kthread.
@@ -207,6 +212,9 @@ BPF_CALL_5(bpf_trace_printk, char *, fmt, u32, fmt_size, u64, arg1,
char buf[64];
int i;
+ if (kernel_is_locked_down("BPF", LOCKDOWN_CONFIDENTIALITY))
+ return -EINVAL;
+
/*
* bpf_check()->check_func_arg()->check_stack_boundary()
* guarantees that fmt points to bpf program stack,
@@ -535,6 +543,9 @@ BPF_CALL_3(bpf_probe_read_str, void *, dst, u32, size,
{
int ret;
+ if (kernel_is_locked_down("BPF", LOCKDOWN_CONFIDENTIALITY))
+ return -EINVAL;
+
/*
* The strncpy_from_unsafe() call will likely not fill the entire
* buffer, but that's okay in this circumstance as we're probing
--
2.21.0.392.gf8f6787159e-goog
From: David Howells <[email protected]>
Disallow opening of debugfs files that might be used to muck around when
the kernel is locked down as various drivers give raw access to hardware
through debugfs. Given the effort of auditing all 2000 or so files and
manually fixing each one as necessary, I've chosen to apply a heuristic
instead. The following changes are made:
(1) chmod and chown are disallowed on debugfs objects (though the root dir
can be modified by mount and remount, but I'm not worried about that).
(2) When the kernel is locked down, only files with the following criteria
are permitted to be opened:
- The file must have mode 00444
- The file must not have ioctl methods
- The file must not have mmap
(3) When the kernel is locked down, files may only be opened for reading.
Normal device interaction should be done through configfs, sysfs or a
miscdev, not debugfs.
Note that this makes it unnecessary to specifically lock down show_dsts(),
show_devs() and show_call() in the asus-wmi driver.
I would actually prefer to lock down all files by default and have the
the files unlocked by the creator. This is tricky to manage correctly,
though, as there are 19 creation functions and ~1600 call sites (some of
them in loops scanning tables).
Signed-off-by: David Howells <[email protected]>
cc: Andy Shevchenko <[email protected]>
cc: [email protected]
cc: [email protected]
cc: Matthew Garrett <[email protected]>
cc: Thomas Gleixner <[email protected]>
Signed-off-by: Matthew Garrett <[email protected]>
---
fs/debugfs/file.c | 28 ++++++++++++++++++++++++++++
fs/debugfs/inode.c | 30 ++++++++++++++++++++++++++++--
2 files changed, 56 insertions(+), 2 deletions(-)
diff --git a/fs/debugfs/file.c b/fs/debugfs/file.c
index 4fce1da7db23..2d18e7711fca 100644
--- a/fs/debugfs/file.c
+++ b/fs/debugfs/file.c
@@ -136,6 +136,25 @@ void debugfs_file_put(struct dentry *dentry)
}
EXPORT_SYMBOL_GPL(debugfs_file_put);
+/*
+ * Only permit access to world-readable files when the kernel is locked down.
+ * We also need to exclude any file that has ways to write or alter it as root
+ * can bypass the permissions check.
+ */
+static bool debugfs_is_locked_down(struct inode *inode,
+ struct file *filp,
+ const struct file_operations *real_fops)
+{
+ if ((inode->i_mode & 07777) == 0444 &&
+ !(filp->f_mode & FMODE_WRITE) &&
+ !real_fops->unlocked_ioctl &&
+ !real_fops->compat_ioctl &&
+ !real_fops->mmap)
+ return false;
+
+ return kernel_is_locked_down("debugfs", LOCKDOWN_INTEGRITY);
+}
+
static int open_proxy_open(struct inode *inode, struct file *filp)
{
struct dentry *dentry = F_DENTRY(filp);
@@ -147,6 +166,11 @@ static int open_proxy_open(struct inode *inode, struct file *filp)
return r == -EIO ? -ENOENT : r;
real_fops = debugfs_real_fops(filp);
+
+ r = -EPERM;
+ if (debugfs_is_locked_down(inode, filp, real_fops))
+ goto out;
+
real_fops = fops_get(real_fops);
if (!real_fops) {
/* Huh? Module did not clean up after itself at exit? */
@@ -272,6 +296,10 @@ static int full_proxy_open(struct inode *inode, struct file *filp)
return r == -EIO ? -ENOENT : r;
real_fops = debugfs_real_fops(filp);
+ r = -EPERM;
+ if (debugfs_is_locked_down(inode, filp, real_fops))
+ goto out;
+
real_fops = fops_get(real_fops);
if (!real_fops) {
/* Huh? Module did not cleanup after itself at exit? */
diff --git a/fs/debugfs/inode.c b/fs/debugfs/inode.c
index 13b01351dd1c..4b877cb1431d 100644
--- a/fs/debugfs/inode.c
+++ b/fs/debugfs/inode.c
@@ -32,6 +32,31 @@ static struct vfsmount *debugfs_mount;
static int debugfs_mount_count;
static bool debugfs_registered;
+/*
+ * Don't allow access attributes to be changed whilst the kernel is locked down
+ * so that we can use the file mode as part of a heuristic to determine whether
+ * to lock down individual files.
+ */
+static int debugfs_setattr(struct dentry *dentry, struct iattr *ia)
+{
+ if ((ia->ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID)) &&
+ kernel_is_locked_down("debugfs", LOCKDOWN_INTEGRITY))
+ return -EPERM;
+ return simple_setattr(dentry, ia);
+}
+
+static const struct inode_operations debugfs_file_inode_operations = {
+ .setattr = debugfs_setattr,
+};
+static const struct inode_operations debugfs_dir_inode_operations = {
+ .lookup = simple_lookup,
+ .setattr = debugfs_setattr,
+};
+static const struct inode_operations debugfs_symlink_inode_operations = {
+ .get_link = simple_get_link,
+ .setattr = debugfs_setattr,
+};
+
static struct inode *debugfs_get_inode(struct super_block *sb)
{
struct inode *inode = new_inode(sb);
@@ -356,6 +381,7 @@ static struct dentry *__debugfs_create_file(const char *name, umode_t mode,
inode->i_mode = mode;
inode->i_private = data;
+ inode->i_op = &debugfs_file_inode_operations;
inode->i_fop = proxy_fops;
dentry->d_fsdata = (void *)((unsigned long)real_fops |
DEBUGFS_FSDATA_IS_REAL_FOPS_BIT);
@@ -513,7 +539,7 @@ struct dentry *debugfs_create_dir(const char *name, struct dentry *parent)
return failed_creating(dentry);
inode->i_mode = S_IFDIR | S_IRWXU | S_IRUGO | S_IXUGO;
- inode->i_op = &simple_dir_inode_operations;
+ inode->i_op = &debugfs_dir_inode_operations;
inode->i_fop = &simple_dir_operations;
/* directory inodes start off with i_nlink == 2 (for "." entry) */
@@ -608,7 +634,7 @@ struct dentry *debugfs_create_symlink(const char *name, struct dentry *parent,
return failed_creating(dentry);
}
inode->i_mode = S_IFLNK | S_IRWXUGO;
- inode->i_op = &simple_symlink_inode_operations;
+ inode->i_op = &debugfs_symlink_inode_operations;
inode->i_link = link;
d_instantiate(dentry, inode);
return end_creating(dentry);
--
2.21.0.392.gf8f6787159e-goog
Tracefs may release more information about the kernel than desirable, so
restrict it when the kernel is locked down in confidentiality mode by
preventing open().
Signed-off-by: Matthew Garrett <[email protected]>
Cc: Steven Rostedt <[email protected]>
---
fs/tracefs/inode.c | 40 +++++++++++++++++++++++++++++++++++++++-
1 file changed, 39 insertions(+), 1 deletion(-)
diff --git a/fs/tracefs/inode.c b/fs/tracefs/inode.c
index 7098c49f3693..576327ffd9d1 100644
--- a/fs/tracefs/inode.c
+++ b/fs/tracefs/inode.c
@@ -31,6 +31,21 @@ static struct vfsmount *tracefs_mount;
static int tracefs_mount_count;
static bool tracefs_registered;
+static int default_open_file(struct inode *inode, struct file *filp)
+{
+ struct dentry *dentry = filp->f_path.dentry;
+ struct file_operations *real_fops;
+
+ if (!dentry)
+ return -EINVAL;
+
+ if (kernel_is_locked_down("tracefs", LOCKDOWN_CONFIDENTIALITY))
+ return -EPERM;
+
+ real_fops = dentry->d_fsdata;
+ return real_fops->open(inode, filp);
+}
+
static ssize_t default_read_file(struct file *file, char __user *buf,
size_t count, loff_t *ppos)
{
@@ -50,6 +65,13 @@ static const struct file_operations tracefs_file_operations = {
.llseek = noop_llseek,
};
+static const struct file_operations tracefs_proxy_file_operations = {
+ .read = default_read_file,
+ .write = default_write_file,
+ .open = default_open_file,
+ .llseek = noop_llseek,
+};
+
static struct tracefs_dir_ops {
int (*mkdir)(const char *name);
int (*rmdir)(const char *name);
@@ -225,6 +247,12 @@ static int tracefs_apply_options(struct super_block *sb)
return 0;
}
+static void tracefs_destroy_inode(struct inode *inode)
+{
+ if S_ISREG(inode->i_mode)
+ kfree(inode->i_fop);
+}
+
static int tracefs_remount(struct super_block *sb, int *flags, char *data)
{
int err;
@@ -260,6 +288,7 @@ static int tracefs_show_options(struct seq_file *m, struct dentry *root)
static const struct super_operations tracefs_super_operations = {
.statfs = simple_statfs,
+ .destroy_inode = tracefs_destroy_inode,
.remount_fs = tracefs_remount,
.show_options = tracefs_show_options,
};
@@ -393,6 +422,7 @@ struct dentry *tracefs_create_file(const char *name, umode_t mode,
{
struct dentry *dentry;
struct inode *inode;
+ struct file_operations *proxy_fops;
if (!(mode & S_IFMT))
mode |= S_IFREG;
@@ -406,8 +436,16 @@ struct dentry *tracefs_create_file(const char *name, umode_t mode,
if (unlikely(!inode))
return failed_creating(dentry);
+ proxy_fops = kzalloc(sizeof(struct file_operations), GFP_KERNEL);
+ if (!proxy_fops)
+ return failed_creating(dentry);
+
+ dentry->d_fsdata = fops ? (void *)fops :
+ (void *)&tracefs_file_operations;
+ memcpy(proxy_fops, dentry->d_fsdata, sizeof(struct file_operations));
+ proxy_fops->open = default_open_file;
inode->i_mode = mode;
- inode->i_fop = fops ? fops : &tracefs_file_operations;
+ inode->i_fop = proxy_fops;
inode->i_private = data;
d_instantiate(dentry, inode);
fsnotify_create(dentry->d_parent->d_inode, dentry);
--
2.21.0.392.gf8f6787159e-goog
Print the content of current->comm in messages generated by lockdown to
indicate a restriction that was hit. This makes it a bit easier to find
out what caused the message.
The message now patterned something like:
Lockdown: <comm>: <what> is restricted; see man kernel_lockdown.7
Signed-off-by: David Howells <[email protected]>
Signed-off-by: Matthew Garrett <[email protected]>
---
security/lock_down.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/security/lock_down.c b/security/lock_down.c
index 9913fff09ad0..2659722784cc 100644
--- a/security/lock_down.c
+++ b/security/lock_down.c
@@ -70,8 +70,8 @@ bool __kernel_is_locked_down(const char *what, enum lockdown_level level,
bool first)
{
if ((kernel_locked_down >= level) && what && first)
- pr_notice("Lockdown: %s is restricted; see man kernel_lockdown.7\n",
- what);
+ pr_notice("Lockdown: %s: %s is restricted; see man kernel_lockdown.7\n",
+ current->comm, what);
return (kernel_locked_down >= level);
}
EXPORT_SYMBOL(__kernel_is_locked_down);
--
2.21.0.392.gf8f6787159e-goog
Systems in lockdown mode should block the kexec of untrusted kernels.
For x86 and ARM we can ensure that a kernel is trustworthy by validating
a PE signature, but this isn't possible on other architectures. On those
platforms we can use IMA digital signatures instead. Add a function to
determine whether IMA has or will verify signatures for a given event type,
and if so permit kexec_file() even if the kernel is otherwise locked down.
This is restricted to cases where CONFIG_INTEGRITY_TRUSTED_KEYRING is set
in order to prevent an attacker from loading additional keys at runtime.
Signed-off-by: Matthew Garrett <[email protected]>
Acked-by: Mimi Zohar <[email protected]>
Cc: Dmitry Kasatkin <[email protected]>
Cc: [email protected]
---
include/linux/ima.h | 9 ++++++
kernel/kexec_file.c | 7 +++-
security/integrity/ima/ima.h | 2 ++
security/integrity/ima/ima_main.c | 2 +-
security/integrity/ima/ima_policy.c | 50 +++++++++++++++++++++++++++++
5 files changed, 68 insertions(+), 2 deletions(-)
diff --git a/include/linux/ima.h b/include/linux/ima.h
index b5e16b8c50b7..60007b86f4fc 100644
--- a/include/linux/ima.h
+++ b/include/linux/ima.h
@@ -127,4 +127,13 @@ static inline int ima_inode_removexattr(struct dentry *dentry,
return 0;
}
#endif /* CONFIG_IMA_APPRAISE */
+
+#if defined(CONFIG_IMA_APPRAISE) && defined(CONFIG_INTEGRITY_TRUSTED_KEYRING)
+extern bool ima_appraise_signature(enum kernel_read_file_id func);
+#else
+static inline bool ima_appraise_signature(enum kernel_read_file_id func)
+{
+ return false;
+}
+#endif /* CONFIG_IMA_APPRAISE && CONFIG_INTEGRITY_TRUSTED_KEYRING */
#endif /* _LINUX_IMA_H */
diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c
index a1cc37c8b43b..7599039623a7 100644
--- a/kernel/kexec_file.c
+++ b/kernel/kexec_file.c
@@ -240,7 +240,12 @@ kimage_file_prepare_segments(struct kimage *image, int kernel_fd, int initrd_fd,
ret = 0;
- if (kernel_is_locked_down(reason, LOCKDOWN_INTEGRITY)) {
+ /* If IMA is guaranteed to appraise a signature on the kexec
+ * image, permit it even if the kernel is otherwise locked
+ * down.
+ */
+ if (!ima_appraise_signature(READING_KEXEC_IMAGE) &&
+ kernel_is_locked_down(reason, LOCKDOWN_INTEGRITY)) {
ret = -EPERM;
goto out;
}
diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h
index cc12f3449a72..fe03cc6f1ca4 100644
--- a/security/integrity/ima/ima.h
+++ b/security/integrity/ima/ima.h
@@ -115,6 +115,8 @@ struct ima_kexec_hdr {
u64 count;
};
+extern const int read_idmap[];
+
#ifdef CONFIG_HAVE_IMA_KEXEC
void ima_load_kexec_buffer(void);
#else
diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c
index 4ffac4f5c647..106f06dee9d1 100644
--- a/security/integrity/ima/ima_main.c
+++ b/security/integrity/ima/ima_main.c
@@ -442,7 +442,7 @@ int ima_read_file(struct file *file, enum kernel_read_file_id read_id)
return 0;
}
-static const int read_idmap[READING_MAX_ID] = {
+const int read_idmap[READING_MAX_ID] = {
[READING_FIRMWARE] = FIRMWARE_CHECK,
[READING_FIRMWARE_PREALLOC_BUFFER] = FIRMWARE_CHECK,
[READING_MODULE] = MODULE_CHECK,
diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c
index 122797023bdb..f8f1cdb74a4f 100644
--- a/security/integrity/ima/ima_policy.c
+++ b/security/integrity/ima/ima_policy.c
@@ -1341,3 +1341,53 @@ int ima_policy_show(struct seq_file *m, void *v)
return 0;
}
#endif /* CONFIG_IMA_READ_POLICY */
+
+#if defined(CONFIG_IMA_APPRAISE) && defined(CONFIG_INTEGRITY_TRUSTED_KEYRING)
+/*
+ * ima_appraise_signature: whether IMA will appraise a given function using
+ * an IMA digital signature. This is restricted to cases where the kernel
+ * has a set of built-in trusted keys in order to avoid an attacker simply
+ * loading additional keys.
+ */
+bool ima_appraise_signature(enum kernel_read_file_id id)
+{
+ struct ima_rule_entry *entry;
+ bool found = false;
+ enum ima_hooks func;
+
+ if (id >= READING_MAX_ID)
+ return false;
+
+ func = read_idmap[id] ?: FILE_CHECK;
+
+ rcu_read_lock();
+ list_for_each_entry_rcu(entry, ima_rules, list) {
+ if (entry->action != APPRAISE)
+ continue;
+
+ /*
+ * A generic entry will match, but otherwise require that it
+ * match the func we're looking for
+ */
+ if (entry->func && entry->func != func)
+ continue;
+
+ /*
+ * We require this to be a digital signature, not a raw IMA
+ * hash.
+ */
+ if (entry->flags & IMA_DIGSIG_REQUIRED)
+ found = true;
+
+ /*
+ * We've found a rule that matches, so break now even if it
+ * didn't require a digital signature - a later rule that does
+ * won't override it, so would be a false positive.
+ */
+ break;
+ }
+
+ rcu_read_unlock();
+ return found;
+}
+#endif /* CONFIG_IMA_APPRAISE && CONFIG_INTEGRITY_TRUSTED_KEYRING */
--
2.21.0.392.gf8f6787159e-goog
From: David Howells <[email protected]>
Disallow the use of certain perf facilities that might allow userspace to
access kernel data.
Signed-off-by: David Howells <[email protected]>
Signed-off-by: Matthew Garrett <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Arnaldo Carvalho de Melo <[email protected]>
---
kernel/events/core.c | 6 ++++++
1 file changed, 6 insertions(+)
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 3cd13a30f732..6ad3d83c091c 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -10461,6 +10461,12 @@ SYSCALL_DEFINE5(perf_event_open,
return -EINVAL;
}
+ if ((attr.sample_type & PERF_SAMPLE_REGS_INTR) &&
+ kernel_is_locked_down("PERF_SAMPLE_REGS_INTR",
+ LOCKDOWN_CONFIDENTIALITY))
+ /* REGS_INTR can leak data, lockdown must prevent this */
+ return -EPERM;
+
/* Only privileged users can get physical addresses */
if ((attr.sample_type & PERF_SAMPLE_PHYS_ADDR) &&
perf_paranoid_kernel() && !capable(CAP_SYS_ADMIN))
--
2.21.0.392.gf8f6787159e-goog
From: David Howells <[email protected]>
Disallow the creation of perf and ftrace kprobes when the kernel is
locked down in confidentiality mode by preventing their registration.
This prevents kprobes from being used to access kernel memory to steal
crypto data, but continues to allow the use of kprobes from signed
modules.
Reported-by: Alexei Starovoitov <[email protected]>
Signed-off-by: David Howells <[email protected]>
Signed-off-by: Matthew Garrett <[email protected]>
Cc: Naveen N. Rao <[email protected]>
Cc: Anil S Keshavamurthy <[email protected]>
Cc: [email protected]
Cc: Masami Hiramatsu <[email protected]>
---
kernel/trace/trace_kprobe.c | 3 +++
1 file changed, 3 insertions(+)
diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
index d5fb09ebba8b..5c70acd80344 100644
--- a/kernel/trace/trace_kprobe.c
+++ b/kernel/trace/trace_kprobe.c
@@ -420,6 +420,9 @@ static int __register_trace_kprobe(struct trace_kprobe *tk)
{
int i, ret;
+ if (kernel_is_locked_down("Use of kprobes", LOCKDOWN_CONFIDENTIALITY))
+ return -EPERM;
+
if (trace_probe_is_registered(&tk->tp))
return -EINVAL;
--
2.21.0.392.gf8f6787159e-goog
From: David Howells <[email protected]>
The testmmiotrace module shouldn't be permitted when the kernel is locked
down as it can be used to arbitrarily read and write MMIO space. This is
a runtime check rather than buildtime in order to allow configurations
where the same kernel may be run in both locked down or permissive modes
depending on local policy.
Suggested-by: Thomas Gleixner <[email protected]>
Signed-off-by: David Howells <[email protected]
Signed-off-by: Matthew Garrett <[email protected]>
cc: Thomas Gleixner <[email protected]>
cc: Steven Rostedt <[email protected]>
cc: Ingo Molnar <[email protected]>
cc: "H. Peter Anvin" <[email protected]>
cc: [email protected]
---
arch/x86/mm/testmmiotrace.c | 3 +++
1 file changed, 3 insertions(+)
diff --git a/arch/x86/mm/testmmiotrace.c b/arch/x86/mm/testmmiotrace.c
index f6ae6830b341..9e8ad665f354 100644
--- a/arch/x86/mm/testmmiotrace.c
+++ b/arch/x86/mm/testmmiotrace.c
@@ -115,6 +115,9 @@ static int __init init(void)
{
unsigned long size = (read_far) ? (8 << 20) : (16 << 10);
+ if (kernel_is_locked_down("MMIO trace testing", LOCKDOWN_INTEGRITY))
+ return -EPERM;
+
if (mmio_address == 0) {
pr_err("you have to use the module argument mmio_address.\n");
pr_err("DO NOT LOAD THIS MODULE UNLESS YOU REALLY KNOW WHAT YOU ARE DOING!\n");
--
2.21.0.392.gf8f6787159e-goog
From: David Howells <[email protected]>
Lock down TIOCSSERIAL as that can be used to change the ioport and irq
settings on a serial port. This only appears to be an issue for the serial
drivers that use the core serial code. All other drivers seem to either
ignore attempts to change port/irq or give an error.
Reported-by: Greg Kroah-Hartman <[email protected]>
Signed-off-by: David Howells <[email protected]>
Signed-off-by: Matthew Garrett <[email protected]>
cc: Jiri Slaby <[email protected]>
Cc: [email protected]
---
drivers/tty/serial/serial_core.c | 6 ++++++
1 file changed, 6 insertions(+)
diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
index d4cca5bdaf1c..65b67f0d4386 100644
--- a/drivers/tty/serial/serial_core.c
+++ b/drivers/tty/serial/serial_core.c
@@ -842,6 +842,12 @@ static int uart_set_info(struct tty_struct *tty, struct tty_port *port,
new_flags = (__force upf_t)new_info->flags;
old_custom_divisor = uport->custom_divisor;
+ if ((change_port || change_irq) &&
+ kernel_is_locked_down("Using TIOCSSERIAL to change device addresses, irqs and dma channels", LOCKDOWN_INTEGRITY)) {
+ retval = -EPERM;
+ goto exit;
+ }
+
if (!capable(CAP_SYS_ADMIN)) {
retval = -EPERM;
if (change_irq || change_port ||
--
2.21.0.392.gf8f6787159e-goog
From: David Howells <[email protected]>
Provided an annotation for module parameters that specify hardware
parameters (such as io ports, iomem addresses, irqs, dma channels, fixed
dma buffers and other types).
Suggested-by: Alan Cox <[email protected]>
Signed-off-by: David Howells <[email protected]>
Signed-off-by: Matthew Garrett <[email protected]>
---
kernel/params.c | 26 +++++++++++++++++++++-----
1 file changed, 21 insertions(+), 5 deletions(-)
diff --git a/kernel/params.c b/kernel/params.c
index ce89f757e6da..da1297f7cc26 100644
--- a/kernel/params.c
+++ b/kernel/params.c
@@ -108,13 +108,19 @@ bool parameq(const char *a, const char *b)
return parameqn(a, b, strlen(a)+1);
}
-static void param_check_unsafe(const struct kernel_param *kp)
+static bool param_check_unsafe(const struct kernel_param *kp,
+ const char *doing)
{
if (kp->flags & KERNEL_PARAM_FL_UNSAFE) {
pr_notice("Setting dangerous option %s - tainting kernel\n",
kp->name);
add_taint(TAINT_USER, LOCKDEP_STILL_OK);
}
+
+ if (kp->flags & KERNEL_PARAM_FL_HWPARAM &&
+ kernel_is_locked_down("Command line-specified device addresses, irqs and dma channels", LOCKDOWN_INTEGRITY))
+ return false;
+ return true;
}
static int parse_one(char *param,
@@ -144,8 +150,10 @@ static int parse_one(char *param,
pr_debug("handling %s with %p\n", param,
params[i].ops->set);
kernel_param_lock(params[i].mod);
- param_check_unsafe(¶ms[i]);
- err = params[i].ops->set(val, ¶ms[i]);
+ if (param_check_unsafe(¶ms[i], doing))
+ err = params[i].ops->set(val, ¶ms[i]);
+ else
+ err = -EPERM;
kernel_param_unlock(params[i].mod);
return err;
}
@@ -553,6 +561,12 @@ static ssize_t param_attr_show(struct module_attribute *mattr,
return count;
}
+#ifdef CONFIG_MODULES
+#define mod_name(mod) (mod)->name
+#else
+#define mod_name(mod) "unknown"
+#endif
+
/* sysfs always hands a nul-terminated string in buf. We rely on that. */
static ssize_t param_attr_store(struct module_attribute *mattr,
struct module_kobject *mk,
@@ -565,8 +579,10 @@ static ssize_t param_attr_store(struct module_attribute *mattr,
return -EPERM;
kernel_param_lock(mk->mod);
- param_check_unsafe(attribute->param);
- err = attribute->param->ops->set(buf, attribute->param);
+ if (param_check_unsafe(attribute->param, mod_name(mk->mod)))
+ err = attribute->param->ops->set(buf, attribute->param);
+ else
+ err = -EPERM;
kernel_param_unlock(mk->mod);
if (!err)
return len;
--
2.21.0.392.gf8f6787159e-goog
From: Matthew Garrett <[email protected]>
custom_method effectively allows arbitrary access to system memory, making
it possible for an attacker to circumvent restrictions on module loading.
Disable it if the kernel is locked down.
Signed-off-by: Matthew Garrett <[email protected]>
Signed-off-by: David Howells <[email protected]>
cc: [email protected]
---
drivers/acpi/custom_method.c | 3 +++
1 file changed, 3 insertions(+)
diff --git a/drivers/acpi/custom_method.c b/drivers/acpi/custom_method.c
index 4451877f83b6..37de3cd84493 100644
--- a/drivers/acpi/custom_method.c
+++ b/drivers/acpi/custom_method.c
@@ -29,6 +29,9 @@ static ssize_t cm_write(struct file *file, const char __user * user_buf,
struct acpi_table_header table;
acpi_status status;
+ if (kernel_is_locked_down("ACPI custom methods", LOCKDOWN_INTEGRITY))
+ return -EPERM;
+
if (!(*ppos)) {
/* parse the table header to get the table length */
if (count <= sizeof(struct acpi_table_header))
--
2.21.0.392.gf8f6787159e-goog
From: Josh Boyer <[email protected]>
This option allows userspace to pass the RSDP address to the kernel, which
makes it possible for a user to modify the workings of hardware . Reject
the option when the kernel is locked down.
Signed-off-by: Josh Boyer <[email protected]>
Signed-off-by: David Howells <[email protected]>
Signed-off-by: Matthew Garrett <[email protected]>
cc: Dave Young <[email protected]>
cc: [email protected]
---
drivers/acpi/osl.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/drivers/acpi/osl.c b/drivers/acpi/osl.c
index f29e427d0d1d..cd5bba7b8eb3 100644
--- a/drivers/acpi/osl.c
+++ b/drivers/acpi/osl.c
@@ -194,7 +194,8 @@ acpi_physical_address __init acpi_os_get_root_pointer(void)
acpi_physical_address pa;
#ifdef CONFIG_KEXEC
- if (acpi_rsdp)
+ if (acpi_rsdp && !kernel_is_locked_down("ACPI RSDP specification",
+ LOCKDOWN_INTEGRITY))
return acpi_rsdp;
#endif
pa = acpi_arch_get_root_pointer();
--
2.21.0.392.gf8f6787159e-goog
From: Jiri Bohac <[email protected]>
When KEXEC_SIG is not enabled, kernel should not load images through
kexec_file systemcall if the kernel is locked down.
[Modified by David Howells to fit with modifications to the previous patch
and to return -EPERM if the kernel is locked down for consistency with
other lockdowns. Modified by Matthew Garrett to remove the IMA
integration, which will be replaced by integrating with the IMA
architecture policy patches.]
Signed-off-by: Jiri Bohac <[email protected]>
Signed-off-by: David Howells <[email protected]>
Signed-off-by: Matthew Garrett <[email protected]>
Reviewed-by: Jiri Bohac <[email protected]>
cc: [email protected]
---
kernel/kexec_file.c | 6 ++++++
1 file changed, 6 insertions(+)
diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c
index 67f3a866eabe..a1cc37c8b43b 100644
--- a/kernel/kexec_file.c
+++ b/kernel/kexec_file.c
@@ -239,6 +239,12 @@ kimage_file_prepare_segments(struct kimage *image, int kernel_fd, int initrd_fd,
}
ret = 0;
+
+ if (kernel_is_locked_down(reason, LOCKDOWN_INTEGRITY)) {
+ ret = -EPERM;
+ goto out;
+ }
+
break;
/* All other errors are fatal, including nomem, unparseable
--
2.21.0.392.gf8f6787159e-goog
From: Dave Young <[email protected]>
Kexec reboot in case secure boot being enabled does not keep the secure
boot mode in new kernel, so later one can load unsigned kernel via legacy
kexec_load. In this state, the system is missing the protections provided
by secure boot.
Adding a patch to fix this by retain the secure_boot flag in original
kernel.
secure_boot flag in boot_params is set in EFI stub, but kexec bypasses the
stub. Fixing this issue by copying secure_boot flag across kexec reboot.
Signed-off-by: Dave Young <[email protected]>
Signed-off-by: David Howells <[email protected]>
Signed-off-by: Matthew Garrett <[email protected]>
cc: [email protected]
---
arch/x86/kernel/kexec-bzimage64.c | 1 +
1 file changed, 1 insertion(+)
diff --git a/arch/x86/kernel/kexec-bzimage64.c b/arch/x86/kernel/kexec-bzimage64.c
index 278cd07228dd..d49554b948fd 100644
--- a/arch/x86/kernel/kexec-bzimage64.c
+++ b/arch/x86/kernel/kexec-bzimage64.c
@@ -179,6 +179,7 @@ setup_efi_state(struct boot_params *params, unsigned long params_load_addr,
if (efi_enabled(EFI_OLD_MEMMAP))
return 0;
+ params->secure_boot = boot_params.secure_boot;
ei->efi_loader_signature = current_ei->efi_loader_signature;
ei->efi_systab = current_ei->efi_systab;
ei->efi_systab_hi = current_ei->efi_systab_hi;
--
2.21.0.392.gf8f6787159e-goog
From: Matthew Garrett <[email protected]>
The kexec_load() syscall permits the loading and execution of arbitrary
code in ring 0, which is something that lock-down is meant to prevent. It
makes sense to disable kexec_load() in this situation.
This does not affect kexec_file_load() syscall which can check for a
signature on the image to be booted.
Signed-off-by: David Howells <[email protected]>
Signed-off-by: Matthew Garrett <[email protected]>
Acked-by: Dave Young <[email protected]>
cc: [email protected]
---
kernel/kexec.c | 8 ++++++++
1 file changed, 8 insertions(+)
diff --git a/kernel/kexec.c b/kernel/kexec.c
index 68559808fdfa..57047acc9a36 100644
--- a/kernel/kexec.c
+++ b/kernel/kexec.c
@@ -207,6 +207,14 @@ static inline int kexec_load_check(unsigned long nr_segments,
if (result < 0)
return result;
+ /*
+ * kexec can be used to circumvent module loading restrictions, so
+ * prevent loading in that case
+ */
+ if (kernel_is_locked_down("kexec of unsigned images",
+ LOCKDOWN_INTEGRITY))
+ return -EPERM;
+
/*
* Verify we have a legal set of flags
* This leaves us room for future extensions.
--
2.21.0.392.gf8f6787159e-goog
From: Matthew Garrett <[email protected]>
uswsusp allows a user process to dump and then restore kernel state, which
makes it possible to modify the running kernel. Disable this if the kernel
is locked down.
Signed-off-by: David Howells <[email protected]>
Signed-off-by: Matthew Garrett <[email protected]>
cc: [email protected]
Cc: [email protected]
Cc: [email protected]
---
kernel/power/user.c | 3 +++
1 file changed, 3 insertions(+)
diff --git a/kernel/power/user.c b/kernel/power/user.c
index 2d8b60a3c86b..99e13fd13237 100644
--- a/kernel/power/user.c
+++ b/kernel/power/user.c
@@ -52,6 +52,9 @@ static int snapshot_open(struct inode *inode, struct file *filp)
if (!hibernation_available())
return -EPERM;
+ if (kernel_is_locked_down("/dev/snapshot", LOCKDOWN_INTEGRITY))
+ return -EPERM;
+
lock_system_sleep();
if (!atomic_add_unless(&snapshot_device_available, -1, 0)) {
--
2.21.0.392.gf8f6787159e-goog
On Wed, 3 Apr 2019 17:32:41 -0700
Matthew Garrett <[email protected]> wrote:
> From: David Howells <[email protected]>
>
> The testmmiotrace module shouldn't be permitted when the kernel is locked
> down as it can be used to arbitrarily read and write MMIO space. This is
> a runtime check rather than buildtime in order to allow configurations
> where the same kernel may be run in both locked down or permissive modes
> depending on local policy.
>
> Suggested-by: Thomas Gleixner <[email protected]>
> Signed-off-by: David Howells <[email protected]
> Signed-off-by: Matthew Garrett <[email protected]>
> cc: Thomas Gleixner <[email protected]>
> cc: Steven Rostedt <[email protected]>
Acked-by: Steven Rostedt (VMware) <[email protected]>
-- Steve
> cc: Ingo Molnar <[email protected]>
> cc: "H. Peter Anvin" <[email protected]>
> cc: [email protected]
> ---
> arch/x86/mm/testmmiotrace.c | 3 +++
> 1 file changed, 3 insertions(+)
>
> diff --git a/arch/x86/mm/testmmiotrace.c b/arch/x86/mm/testmmiotrace.c
> index f6ae6830b341..9e8ad665f354 100644
> --- a/arch/x86/mm/testmmiotrace.c
> +++ b/arch/x86/mm/testmmiotrace.c
> @@ -115,6 +115,9 @@ static int __init init(void)
> {
> unsigned long size = (read_far) ? (8 << 20) : (16 << 10);
>
> + if (kernel_is_locked_down("MMIO trace testing", LOCKDOWN_INTEGRITY))
> + return -EPERM;
> +
> if (mmio_address == 0) {
> pr_err("you have to use the module argument mmio_address.\n");
> pr_err("DO NOT LOAD THIS MODULE UNLESS YOU REALLY KNOW WHAT YOU ARE DOING!\n");
On Wed, 3 Apr 2019, Matthew Garrett wrote:
> From: David Howells <[email protected]>
>
> The testmmiotrace module shouldn't be permitted when the kernel is locked
> down as it can be used to arbitrarily read and write MMIO space. This is
> a runtime check rather than buildtime in order to allow configurations
> where the same kernel may be run in both locked down or permissive modes
> depending on local policy.
>
> Suggested-by: Thomas Gleixner <[email protected]>
> Signed-off-by: David Howells <[email protected]
> Signed-off-by: Matthew Garrett <[email protected]>
Reviewed-by: Thomas Gleixner <[email protected]>
On Wed, 3 Apr 2019, Matthew Garrett wrote:
> From: Matthew Garrett <[email protected]>
>
> IO port access would permit users to gain access to PCI configuration
> registers, which in turn (on a lot of hardware) give access to MMIO
> register space. This would potentially permit root to trigger arbitrary
> DMA, so lock it down by default.
>
> This also implicitly locks down the KDADDIO, KDDELIO, KDENABIO and
> KDDISABIO console ioctls.
>
> Signed-off-by: Matthew Garrett <[email protected]>
> Signed-off-by: David Howells <[email protected]>
Reviewed-by: Thomas Gleixner <[email protected]>
On Wed, 3 Apr 2019 17:32:49 -0700
Matthew Garrett <[email protected]> wrote:
> +static void tracefs_destroy_inode(struct inode *inode)
> +{
> + if S_ISREG(inode->i_mode)
Can we please put parenthesis around the condition. I know that the
macro has them, but no other place in the kernel plays such a trick.
if (S_ISREG(inode->i_mode))
Other than that, the rest looks good.
Reviewed-by: Steven Rostedt (VMware) <[email protected]>
-- Steve
> + kfree(inode->i_fop);
> +}
> +
> static int tracefs_remount(struct super_block *sb, int *flags, char *data)
> {
> int err;
> @@ -260,6 +288,7 @@ static int tracefs_show_options(struct seq_file *m, struct dentry *root)
>
> static const struct super_operations tracefs_super_operations = {
> .statfs = simple_statfs,
> + .destroy_inode = tracefs_destroy_inode,
> .remount_fs = tracefs_remount,
> .show_options = tracefs_show_options,
> };
> @@ -393,6 +422,7 @@ struct dentry *tracefs_create_file(const char *name, umode_t mode,
> {
> struct dentry *dentry;
> struct inode *inode;
> + struct file_operations *proxy_fops;
>
> if (!(mode & S_IFMT))
> mode |= S_IFREG;
> @@ -406,8 +436,16 @@ struct dentry *tracefs_create_file(const char *name, umode_t mode,
> if (unlikely(!inode))
> return failed_creating(dentry);
>
> + proxy_fops = kzalloc(sizeof(struct file_operations), GFP_KERNEL);
> + if (!proxy_fops)
> + return failed_creating(dentry);
> +
> + dentry->d_fsdata = fops ? (void *)fops :
> + (void *)&tracefs_file_operations;
> + memcpy(proxy_fops, dentry->d_fsdata, sizeof(struct file_operations));
> + proxy_fops->open = default_open_file;
> inode->i_mode = mode;
> - inode->i_fop = fops ? fops : &tracefs_file_operations;
> + inode->i_fop = proxy_fops;
> inode->i_private = data;
> d_instantiate(dentry, inode);
> fsnotify_create(dentry->d_parent->d_inode, dentry);
On Thu, Apr 4, 2019 at 6:39 AM Steven Rostedt <[email protected]> wrote:
>
> On Wed, 3 Apr 2019 17:32:49 -0700
> Matthew Garrett <[email protected]> wrote:
>
>
> > +static void tracefs_destroy_inode(struct inode *inode)
> > +{
> > + if S_ISREG(inode->i_mode)
>
> Can we please put parenthesis around the condition. I know that the
> macro has them, but no other place in the kernel plays such a trick.
Ha, I've been spending too much time in Go lately. Fixed.
On 4/4/19 11:32 am, Matthew Garrett wrote:
> diff --git a/Documentation/ABI/testing/lockdown b/Documentation/ABI/testing/lockdown
> new file mode 100644
> index 000000000000..5bd51e20917a
> --- /dev/null
> +++ b/Documentation/ABI/testing/lockdown
> @@ -0,0 +1,19 @@
> +What: security/lockdown
> +Date: March 2019
> +Contact: Matthew Garrett <[email protected]>
> +Description:
> + If CONFIG_LOCK_DOWN_KERNEL is enabled, the kernel can be
> + moved to a more locked down state at runtime by writing to
> + this attribute. Valid values are:
> +
> + integrity:
> + The kernel will disable functionality that allows
> + userland to modify the running kernel image, other
> + than through the loading or execution of appropriately
> + signed objects.
> +
> + confidentiality:
> + The kernel will disable all functionality disabled by
> + the integrity mode, but additionally will disable
> + features that potentially permit userland to obtain
> + confidential information stored within the kernel.
[+ linuxppc, mpe, dja, cmr]
I'm thinking about whether we should lock down the powerpc xmon debug
monitor - intuitively, I think the answer is yes if for no other reason
than Least Astonishment, when lockdown is enabled you probably don't
expect xmon to keep letting you access kernel memory.
Semantically though, xmon is not a userspace process - it's in kernel
and reads debug commands/outputs debug data directly from/to the
console. Is that a threat vector that this series cares about?
--
Andrew Donnellan OzLabs, ADL Canberra
[email protected] IBM Australia Limited
Hi Andrew,
>> + If CONFIG_LOCK_DOWN_KERNEL is enabled, the kernel can be
>> + moved to a more locked down state at runtime by writing to
>> + this attribute. Valid values are:
>> +
>> + integrity:
>> + The kernel will disable functionality that allows
>> + userland to modify the running kernel image, other
>> + than through the loading or execution of appropriately
>> + signed objects.
>> +
>> + confidentiality:
>> + The kernel will disable all functionality disabled by
>> + the integrity mode, but additionally will disable
>> + features that potentially permit userland to obtain
>> + confidential information stored within the kernel.
>
> [+ linuxppc, mpe, dja, cmr]
>
> I'm thinking about whether we should lock down the powerpc xmon debug
> monitor - intuitively, I think the answer is yes if for no other reason
> than Least Astonishment, when lockdown is enabled you probably don't
> expect xmon to keep letting you access kernel memory.
>
> Semantically though, xmon is not a userspace process - it's in kernel
> and reads debug commands/outputs debug data directly from/to the
> console. Is that a threat vector that this series cares about?
I guess there are 2 ways you could think about lockdown:
- It adds a security boundary between the kernel and UID 0, so that
userland cannot compromise the integrity/confidentiality of the
locked down kernel.
- It is a bundle of related security boundaries so that the
integrity/confidentiality of a running, locked down kernel cannot be
compromised, even by a privileged, physically present user.
You're right that techincally xmon is in the kernel and on the console
rather than in userland, so it doesn't fall within the first concept of
lockdown. But I think usecases for lockdown tend to expect something
more like the second concept.
IOW, lockdown is a trapdoor - once you've locked down a kernel, you
can't get out of lockdown (except by rebooting). xmon would allow you to
get out of the trapdoor, so I think it should be restricted by lockdown.
Regards,
Daniel
>
>
> --
> Andrew Donnellan OzLabs, ADL Canberra
> [email protected] IBM Australia Limited
On Tue, Apr 16, 2019 at 1:40 AM Andrew Donnellan
<[email protected]> wrote:
> I'm thinking about whether we should lock down the powerpc xmon debug
> monitor - intuitively, I think the answer is yes if for no other reason
> than Least Astonishment, when lockdown is enabled you probably don't
> expect xmon to keep letting you access kernel memory.
The original patchset contained a sysrq hotkey to allow physically
present users to disable lockdown, so I'm not super concerned about
this case - I could definitely be convinced otherwise, though.
Matthew Garrett <[email protected]> writes:
> On Tue, Apr 16, 2019 at 1:40 AM Andrew Donnellan
> <[email protected]> wrote:
>> I'm thinking about whether we should lock down the powerpc xmon debug
>> monitor - intuitively, I think the answer is yes if for no other reason
>> than Least Astonishment, when lockdown is enabled you probably don't
>> expect xmon to keep letting you access kernel memory.
>
> The original patchset contained a sysrq hotkey to allow physically
> present users to disable lockdown, so I'm not super concerned about
> this case - I could definitely be convinced otherwise, though.
So currently (and I'm pretty new to this as I've only recently rejoined
IBM) we aren't considering access to the console to be sufficient to
assert physical presence on bare-metal server-class Power machines. The
short argument for this is that with IPMI and BMCs, a server's console
isn't what it used to be. Our console is also a bit different to x86:
we don't generally have bios configuration screens on the console.
In your example, a sysrq key would allow you to disable lockdown after
the system has booted. On Power though, we use Linux as a bootloader
(Petitboot: https://github.com/open-power/petitboot) so being able to
disable lockdown there allows an IPMI-connected user to prevent a signed
kernel being loaded in the first place. I don't know if this is
_actually_ worse, but it certainly feels worse.
There are of course some arguments against our approach. I'm aware of
some of them. I'm also very open to being told that not equating console
access with physical access is fundamentally silly or broken and that we
should rethink things.
Regards,
Daniel
Hi,
>>> I'm thinking about whether we should lock down the powerpc xmon debug
>>> monitor - intuitively, I think the answer is yes if for no other reason
>>> than Least Astonishment, when lockdown is enabled you probably don't
>>> expect xmon to keep letting you access kernel memory.
>>
>> The original patchset contained a sysrq hotkey to allow physically
>> present users to disable lockdown, so I'm not super concerned about
>> this case - I could definitely be convinced otherwise, though.
So Mimi contacted me offlist and very helpfully provided me with a much
better and less confused justification for disabling xmon in lockdown:
On x86, physical presence (== console access) is a trigger to
disable/enable lockdown mode.
In lockdown mode, you're not supposed to be able to modify memory. xmon
allows you to modify memory, and therefore shouldn't be allowed in
lockdown.
So, if you can disable lockdown on the console that's probably OK, but
it should be specifically disabling lockdown, not randomly editing
memory with xmon.
Regards,
Daniel
Hi James,
What's the best way forward with this? I'm still not entirely clear on
how it can be implemented purely as an LSM, but if you have ideas on
what sort of implementation you'd prefer I'm happy to work on that.
On 29/4/19 2:54 pm, Daniel Axtens wrote:
> Hi,
>
>>>> I'm thinking about whether we should lock down the powerpc xmon debug
>>>> monitor - intuitively, I think the answer is yes if for no other reason
>>>> than Least Astonishment, when lockdown is enabled you probably don't
>>>> expect xmon to keep letting you access kernel memory.
>>>
>>> The original patchset contained a sysrq hotkey to allow physically
>>> present users to disable lockdown, so I'm not super concerned about
>>> this case - I could definitely be convinced otherwise, though.
>
> So Mimi contacted me offlist and very helpfully provided me with a much
> better and less confused justification for disabling xmon in lockdown:
>
> On x86, physical presence (== console access) is a trigger to
> disable/enable lockdown mode.
>
> In lockdown mode, you're not supposed to be able to modify memory. xmon
> allows you to modify memory, and therefore shouldn't be allowed in
> lockdown.
>
> So, if you can disable lockdown on the console that's probably OK, but
> it should be specifically disabling lockdown, not randomly editing
> memory with xmon.
That makes sense.
--
Andrew Donnellan OzLabs, ADL Canberra
[email protected] IBM Australia Limited
+bpf list
On Wed, Apr 3, 2019 at 8:34 PM Matthew Garrett
<[email protected]> wrote:
> There are some bpf functions can be used to read kernel memory:
> bpf_probe_read, bpf_probe_write_user and bpf_trace_printk. These allow
> private keys in kernel memory (e.g. the hibernation image signing key) to
> be read by an eBPF program and kernel memory to be altered without
> restriction. Disable them if the kernel has been locked down in
> confidentiality mode.
>
> Suggested-by: Alexei Starovoitov <[email protected]>
> Signed-off-by: David Howells <[email protected]>
> Signed-off-by: Matthew Garrett <[email protected]>
> cc: [email protected]
> cc: Chun-Yi Lee <[email protected]>
> cc: Alexei Starovoitov <[email protected]>
> Cc: Daniel Borkmann <[email protected]>
> ---
> kernel/trace/bpf_trace.c | 11 +++++++++++
> 1 file changed, 11 insertions(+)
>
> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> index 8b068adb9da1..9e8eda605b5e 100644
> --- a/kernel/trace/bpf_trace.c
> +++ b/kernel/trace/bpf_trace.c
> @@ -137,6 +137,9 @@ BPF_CALL_3(bpf_probe_read, void *, dst, u32, size, const void *, unsafe_ptr)
> {
> int ret;
>
> + if (kernel_is_locked_down("BPF", LOCKDOWN_CONFIDENTIALITY))
> + return -EINVAL;
> +
> ret = probe_kernel_read(dst, unsafe_ptr, size);
> if (unlikely(ret < 0))
> memset(dst, 0, size);
This looks wrong. bpf_probe_read_proto is declared with an
ARG_PTR_TO_UNINIT_MEM argument, so if you don't do a "memset(dst, 0,
size);" like in the probe_kernel_read() error path, the BPF program
can read uninitialized memory.
On Mon, 29 Apr 2019, Matthew Garrett wrote:
> Hi James,
>
> What's the best way forward with this? I'm still not entirely clear on
> how it can be implemented purely as an LSM, but if you have ideas on
> what sort of implementation you'd prefer I'm happy to work on that.
It can't be implemented purely as an LSM.
The concerns I have are:
o Mixing of mechanism and policy (they are hardcoded together)
o Too-coarse policy (all or nothing, which will lead many to choose
nothing)
o Lack of integration with LSM
o Completeness
o Maintenance (including adding new lockdowns without breaking existing
userspace)
One possible direction is to (as previously mentioned) assign IDs to each
callsite and be able to check this ID against a simple policy array
(allow/deny). The default policy choices could be reduced to 'all' or
'none' during kconfig, and allow a custom policy to be loaded later if
desired.
Within the policy check hook, we could add a new LSM hook, which would
allow an LSM to restrictively override the lockdown policy with its own
(so e.g. SELinux could utilize the context of the current process to
determine if a lockdown feature should be enforced).
This doesn't really address the completeness / maintenance issue (i.e. "do
we have everything covered and how do we ensure this on an ongoing
basis?", and "what will this new lockdown feature break?"), although it
should make it easier to add new lockdown callsites as they don't have to
be enabled by the user.
Thoughts?
--
James Morris
<[email protected]>
On Thu, May 2, 2019 at 2:07 PM James Morris <[email protected]> wrote:
> One possible direction is to (as previously mentioned) assign IDs to each
> callsite and be able to check this ID against a simple policy array
> (allow/deny). The default policy choices could be reduced to 'all' or
> 'none' during kconfig, and allow a custom policy to be loaded later if
> desired.
Ok. My primary concern around this is that it's very difficult to use
correctly in anything other than the "all" or "none" modes. If a new
kernel feature is added with integrated lockdown support, if an admin
is simply setting the flags of things they wish to block then this
will be left enabled - and may violate the admin's expectations around
integrity. On the other hand, if an admin is simply setting the flags
of things they wish to permit, then adding lockdown support to an
existing kernel feature may result in that feature suddenly being
disabled, which may also violate the admin's expectations around the
flags providing a stable set of behaviour.
Given that, would you prefer such a policy expression to look like?
> Within the policy check hook, we could add a new LSM hook, which would
> allow an LSM to restrictively override the lockdown policy with its own
Ok, that makes sense. If we take this approach, does there need to be
a separate policy mechanism at all? Users who want fine-grained
control would be able to set the behaviour to "None" and then use
their choice of LSM to express more fine-grained control.
> This doesn't really address the completeness / maintenance issue (i.e. "do
> we have everything covered and how do we ensure this on an ongoing
> basis?", and "what will this new lockdown feature break?"), although it
> should make it easier to add new lockdown callsites as they don't have to
> be enabled by the user.
I can start on this.
On Thu, 2 May 2019, Matthew Garrett wrote:
> On Thu, May 2, 2019 at 2:07 PM James Morris <[email protected]> wrote:
> > One possible direction is to (as previously mentioned) assign IDs to each
> > callsite and be able to check this ID against a simple policy array
> > (allow/deny). The default policy choices could be reduced to 'all' or
> > 'none' during kconfig, and allow a custom policy to be loaded later if
> > desired.
>
> Ok. My primary concern around this is that it's very difficult to use
> correctly in anything other than the "all" or "none" modes. If a new
> kernel feature is added with integrated lockdown support, if an admin
> is simply setting the flags of things they wish to block then this
> will be left enabled - and may violate the admin's expectations around
> integrity. On the other hand, if an admin is simply setting the flags
> of things they wish to permit, then adding lockdown support to an
> existing kernel feature may result in that feature suddenly being
> disabled, which may also violate the admin's expectations around the
> flags providing a stable set of behaviour.
Understood. Most uses will likely be either a distro or an embedded
system, who I'm assuming would provide a useful policy by default, and
perhaps a high-level abstraction for modification.
> Given that, would you prefer such a policy expression to look like?
Perhaps a write-once policy, injected from userspace during early boot?
The policy could be simply a list of:
lockdown_feature true|false
>
> > Within the policy check hook, we could add a new LSM hook, which would
> > allow an LSM to restrictively override the lockdown policy with its own
>
> Ok, that makes sense. If we take this approach, does there need to be
> a separate policy mechanism at all? Users who want fine-grained
> control would be able to set the behaviour to "None" and then use
> their choice of LSM to express more fine-grained control.
Right, and there could be a stackable LSM which just does fine-grained
policy (per above).
>
> > This doesn't really address the completeness / maintenance issue (i.e. "do
> > we have everything covered and how do we ensure this on an ongoing
> > basis?", and "what will this new lockdown feature break?"), although it
> > should make it easier to add new lockdown callsites as they don't have to
> > be enabled by the user.
>
> I can start on this.
Cool!
--
James Morris
<[email protected]>
> On May 2, 2019, at 4:19 PM, James Morris <[email protected]> wrote:
>
>> On Thu, 2 May 2019, Matthew Garrett wrote:
>>
>>> On Thu, May 2, 2019 at 2:07 PM James Morris <[email protected]> wrote:
>>> One possible direction is to (as previously mentioned) assign IDs to each
>>> callsite and be able to check this ID against a simple policy array
>>> (allow/deny). The default policy choices could be reduced to 'all' or
>>> 'none' during kconfig, and allow a custom policy to be loaded later if
>>> desired.
>>
>> Ok. My primary concern around this is that it's very difficult to use
>> correctly in anything other than the "all" or "none" modes. If a new
>> kernel feature is added with integrated lockdown support, if an admin
>> is simply setting the flags of things they wish to block then this
>> will be left enabled - and may violate the admin's expectations around
>> integrity. On the other hand, if an admin is simply setting the flags
>> of things they wish to permit, then adding lockdown support to an
>> existing kernel feature may result in that feature suddenly being
>> disabled, which may also violate the admin's expectations around the
>> flags providing a stable set of behaviour.
>
> Understood. Most uses will likely be either a distro or an embedded
> system, who I'm assuming would provide a useful policy by default, and
> perhaps a high-level abstraction for modification.
>
>> Given that, would you prefer such a policy expression to look like?
>
> Perhaps a write-once policy, injected from userspace during early boot?
>
> The policy could be simply a list of:
>
> lockdown_feature true|false
>
I’m not convinced this is worthwhile. As I see it, there really are only two privileges here: root can read kernel memory, and root can corrupt kernel state. A policy that root can’t corrupt kernel memory except using, say, eBPF is useless — it gives warm fuzzy feelings but nothing else.