This patchset removes livepatch's need for architecture-specific relocation
code by leveraging existing code in the module loader to perform
arch-dependent work. Specifically, instead of duplicating code and
re-implementing what the apply_relocate_add() function in the module loader
already does in livepatch's klp_write_module_reloc(), we reuse
apply_relocate_add() to write relocations. The hope is that this will make
livepatch more easily portable to other architectures and greatly reduce
the amount of arch-specific code required to port livepatch to a particular
architecture.
Background: Why does livepatch need to write its own relocations?
==
A typical livepatch module contains patched versions of functions that can
reference non-exported global symbols and non-included local symbols.
Relocations referencing these types of symbols cannot be left in as-is
since the kernel module loader cannot resolve them and will therefore
reject the livepatch module. Furthermore, we cannot apply relocations that
affect modules not loaded yet at run time (e.g. a patch to a driver). The
current kpatch build system therefore solves this problem by embedding
special "dynrela" (dynamic reloc) sections in the resulting patch module
Elf output. Using these dynrela sections, livepatch can correctly resolve
symbols while taking into account its scope and what module the symbol
belongs to, and then manually apply the dynamic relocations.
Motivation: Why is having arch-dependent relocation code a problem?
==
The original motivation for this patchset stems from the increasing
roadblocks encountered while attempting to port livepatch to s390.
Specifically, there were problems dealing with s390 PLT and GOT relocation
types (R_390_{PLT,GOT}), which are handled differently from x86's
relocation types (which are much simpler to deal with, and a single
livepatch function (klp_write_module_reloc()) has been sufficient enough).
These s390 reloc types cannot be handled by simply performing a calculation
(as in the x86 case). For s390 modules with PLT/GOT relocations, the kernel
module loader allocates and fills in PLT+GOT table entries for every symbol
referenced by a PLT/GOT reloc in module core memory. So the problem of
porting livepatch to s390 became much more complicated than simply writing
an s390-specific klp_write_module_reloc() function. How can livepatch
handle these relocation types if the s390 module loader needs to allocate
and fill PLT/GOT entries ahead of time? The potential solutions were: 1)
have livepatch possibly allocate and maintain its own PLT/GOT tables for
every patch module (requiring even more arch-specific code), 2) modify the
s390 module loader heavily to accommodate livepatch modules (i.e. allocate
all the needed PLT/GOT entries for livepatch in advance but refrain from
applying relocations for to-be-patched modules), or 3) eliminate this
potential mess by leveraging module loader code to do all the relocation
work, letting livepatch off the hook completely. Solution #3 is what this
patchset implements.
How does this patchset remedy these problems?
==
Reusing the module loader code to perform livepatch relocations means that
livepatch no longer needs arch-specific reloc code and the aforementioned
problems with s390 PLT/GOT reloc types disappear (because we let the module
loader do all the relocation work for us). It will enable livepatch to be
more easily ported to other architectures.
Summary of proposed changes
==
This patch series enables livepatch to use the module loader's
apply_relocate_add() function to apply livepatch relocations (i.e. what
used to be dynrelas). apply_relocate_add() requires access to a patch
module's section headers, symbol table, reloc section indices, etc., and all
of these are accessible through the load_info struct used in the module
loader. Therefore we persist module Elf information (copied from load_info)
for livepatch modules.
The ELF-related changes enable livepatch to patch modules that are not yet
loaded (as well as patch vmlinux when kaslr is enabled). In order to use
apply_relocate_add(), we need real SHT_RELA sections to pass in. A
complication here is that relocations for not-yet-loaded modules should not
be applied when the patch module loads; they should only be applied once
the target module is loaded. Thus kpatch build scripts were modified to
output a livepatch module that contains special .klp.rela. sections that
are managed by livepatch and are applied at the appropriate time (i.e. when
target module loads). They are marked with a special SHF_RELA_LIVEPATCH
section flag to indicate to the module loader that livepatch will handle
them. The SHN_LIVEPATCH shndx marks symbols that need to be resolved
once their respective target module loads. So, the module loader ignores
these symbols and does not attempt to resolve them. These ELF constants
were selected from OS-specific ranges according to the definitions from
glibc.
Patches based on linux-next.
Previous patchset (v5) found here:
http://lkml.kernel.org/g/[email protected]
v6:
- Since we hard-code the field widths for the objname and symbol name
for the sscanf() calls, which are supposed to correspond to the values
of MODULE_NAME_LEN and KSYM_NAME_LEN, use BUILD_BUG_ON() to detect when
the values of these constants deviate from the expected values.
- Squash the sample livepatch module patch into patch 4
("livepatch: reuse module loader code to write relocations") so
git bisects don't break
- Don't need the klp_buf struct, just use plain char arrays to hold the
output of sscanf(). Also, no need to clear the bufs after every
invocation, as sscanf() takes care to put a null byte at the end of
the bufs.
- Fix compiler kbuild errors for the !CONFIG_LIVEPATCH case
- Fixed some small module.c nits
v5:
- The '%[' format specifier for sscanf() is now available on linux-next,
so use sscanf() to parse symbol and section names instead of a using
multiple clumsy klp_get_* helper functions and strspn/strcspn calls.
- Removed some unnecessary comments
- For symtab access, just use the core symtab mod->core_kallsyms.symtab
(what used to be mod->core_symtab). If we use mod->kallsyms.symtab
(what used to be mod->symtab), during the patch module init process we
would be using the init symbol table (the one in module init memory)
instead of the core symbol table, because mod->kallsyms only gets reassigned
to mod->core_kallsyms *after* do_one_initcall(). Though in the case of
livepatch modules both the symbol tables in init vs core memory are
identical, I think it is better to be consistent.
v4:
- Way more error checking for all the string manipulation on
livepatch symbol names and sections.
- Handle error conditions such as loading a klp module on a
!CONFIG_LIVEPATCH kernel
- Don't encode sympos in a symbol's st_other field. Instead, append it
to the symbol name in the form .klp.sym.objname.symname,sympos
- Instead of a half initialized copy of the load_info struct in
mod->info, define a livepatch specific struct (klp_modinfo) instead
that contains just the needed Elf info.
- Much more detailed documentation about patch module requirements
and the module elf format.
v3:
- Remove usage of the klp_reloc_sec struct, since we can simply loop
through the patch module's section headers.
- Remove necessity of the "external" flag by prefixing symbol names
with the object name and extracting this name during symbol
resolution.
- Create CONFIG_LIVEPATCH and !CONFIG_LIVEPATCH versions of
{copy,free}_module_elf(), is_livepatch_module(), and
check_livepatch_modinfo().
- Encoded symbol position of a livepatch sym in its st_other field.
- Various bug fixes from v2
v2:
- Copy only the minimum required Elf information for livepatch modules to
make the call to apply_relocate_add(), not the entire load_info struct
and the redundant copy of the module in memory
- Add module->klp flag for simple identification of livepatch modules
- s390: remove redundant vfree() and preserve mod_arch_specific if
livepatch module
- Use array format instead of a linked list for klp_reloc_secs
- Add new documentation describing the format of a livepatch module in
Documentation/livepatch
Jessica Yu (5):
Elf: add livepatch-specific Elf constants
module: preserve Elf information for livepatch modules
module: s390: keep mod_arch_specific for livepatch modules
livepatch: reuse module loader code to write relocations
Documentation: livepatch: outline Elf format and requirements for
patch modules
Documentation/livepatch/module-elf-format.txt | 311 ++++++++++++++++++++++++++
arch/s390/include/asm/livepatch.h | 7 -
arch/s390/kernel/module.c | 6 +-
arch/x86/include/asm/livepatch.h | 2 -
arch/x86/kernel/Makefile | 1 -
arch/x86/kernel/livepatch.c | 70 ------
include/linux/livepatch.h | 20 --
include/linux/module.h | 25 +++
include/uapi/linux/elf.h | 10 +-
kernel/livepatch/core.c | 148 +++++++-----
kernel/module.c | 125 ++++++++++-
samples/livepatch/livepatch-sample.c | 1 +
12 files changed, 563 insertions(+), 163 deletions(-)
create mode 100644 Documentation/livepatch/module-elf-format.txt
delete mode 100644 arch/x86/kernel/livepatch.c
--
2.4.3
Livepatch manages its own relocation sections and symbols in order to be
able to reuse module loader code to write relocations. This removes
livepatch's dependence on separate "dynrela" sections to write relocations
and also allows livepatch to patch modules that are not yet loaded.
The livepatch Elf relocation section flag (SHF_RELA_LIVEPATCH),
and symbol section index (SHN_LIVEPATCH) allow both livepatch and the
module loader to identity livepatch relocation sections and livepatch
symbols.
Livepatch relocation sections are marked with SHF_RELA_LIVEPATCH to
indicate to the module loader that it should not apply that relocation
section and that livepatch will handle them.
The SHN_LIVEPATCH shndx marks symbols that will be resolved by livepatch.
The module loader ignores these symbols and does not attempt to resolve
them.
The values of these Elf constants were selected from OS-specific
ranges according to the definitions from glibc.
Signed-off-by: Jessica Yu <[email protected]>
Reviewed-by: Miroslav Benes <[email protected]>
---
include/uapi/linux/elf.h | 10 ++++++----
1 file changed, 6 insertions(+), 4 deletions(-)
diff --git a/include/uapi/linux/elf.h b/include/uapi/linux/elf.h
index 71e1d0e..cb4a72f 100644
--- a/include/uapi/linux/elf.h
+++ b/include/uapi/linux/elf.h
@@ -282,16 +282,18 @@ typedef struct elf64_phdr {
#define SHT_HIUSER 0xffffffff
/* sh_flags */
-#define SHF_WRITE 0x1
-#define SHF_ALLOC 0x2
-#define SHF_EXECINSTR 0x4
-#define SHF_MASKPROC 0xf0000000
+#define SHF_WRITE 0x1
+#define SHF_ALLOC 0x2
+#define SHF_EXECINSTR 0x4
+#define SHF_RELA_LIVEPATCH 0x00100000
+#define SHF_MASKPROC 0xf0000000
/* special section indexes */
#define SHN_UNDEF 0
#define SHN_LORESERVE 0xff00
#define SHN_LOPROC 0xff00
#define SHN_HIPROC 0xff1f
+#define SHN_LIVEPATCH 0xff20
#define SHN_ABS 0xfff1
#define SHN_COMMON 0xfff2
#define SHN_HIRESERVE 0xffff
--
2.4.3
For livepatch modules, copy Elf section, symbol, and string information
from the load_info struct in the module loader. Persist copies of the
original symbol table and string table.
Livepatch manages its own relocation sections in order to reuse module
loader code to write relocations. Livepatch modules must preserve Elf
information such as section indices in order to apply livepatch relocation
sections using the module loader's apply_relocate_add() function.
In order to apply livepatch relocation sections, livepatch modules must
keep a complete copy of their original symbol table in memory. Normally, a
stripped down copy of a module's symbol table (containing only "core"
symbols) is made available through module->core_symtab. But for livepatch
modules, the symbol table copied into memory on module load must be exactly
the same as the symbol table produced when the patch module was compiled.
This is because the relocations in each livepatch relocation section refer
to their respective symbols with their symbol indices, and the original
symbol indices (and thus the symtab ordering) must be preserved in order
for apply_relocate_add() to find the right symbol.
Signed-off-by: Jessica Yu <[email protected]>
Reviewed-by: Miroslav Benes <[email protected]>
---
include/linux/module.h | 25 ++++++++++
kernel/module.c | 125 +++++++++++++++++++++++++++++++++++++++++++++++--
2 files changed, 147 insertions(+), 3 deletions(-)
diff --git a/include/linux/module.h b/include/linux/module.h
index 2bb0c30..3daf2b3 100644
--- a/include/linux/module.h
+++ b/include/linux/module.h
@@ -330,6 +330,15 @@ struct mod_kallsyms {
char *strtab;
};
+#ifdef CONFIG_LIVEPATCH
+struct klp_modinfo {
+ Elf_Ehdr hdr;
+ Elf_Shdr *sechdrs;
+ char *secstrings;
+ unsigned int symndx;
+};
+#endif
+
struct module {
enum module_state state;
@@ -456,7 +465,11 @@ struct module {
#endif
#ifdef CONFIG_LIVEPATCH
+ bool klp; /* Is this a livepatch module? */
bool klp_alive;
+
+ /* Elf information */
+ struct klp_modinfo *klp_info;
#endif
#ifdef CONFIG_MODULE_UNLOAD
@@ -630,6 +643,18 @@ static inline bool module_requested_async_probing(struct module *module)
return module && module->async_probe_requested;
}
+#ifdef CONFIG_LIVEPATCH
+static inline bool is_livepatch_module(struct module *mod)
+{
+ return mod->klp;
+}
+#else /* !CONFIG_LIVEPATCH */
+static inline bool is_livepatch_module(struct module *mod)
+{
+ return false;
+}
+#endif /* CONFIG_LIVEPATCH */
+
#else /* !CONFIG_MODULES... */
/* Given an address, look for it in the exception tables. */
diff --git a/kernel/module.c b/kernel/module.c
index 041200c..5f71aa6 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -1973,6 +1973,83 @@ static void module_enable_nx(const struct module *mod) { }
static void module_disable_nx(const struct module *mod) { }
#endif
+#ifdef CONFIG_LIVEPATCH
+/*
+ * Persist Elf information about a module. Copy the Elf header,
+ * section header table, section string table, and symtab section
+ * index from info to mod->klp_info.
+ */
+static int copy_module_elf(struct module *mod, struct load_info *info)
+{
+ unsigned int size, symndx;
+ int ret;
+
+ size = sizeof(*mod->klp_info);
+ mod->klp_info = kmalloc(size, GFP_KERNEL);
+ if (mod->klp_info == NULL)
+ return -ENOMEM;
+
+ /* Elf header */
+ size = sizeof(mod->klp_info->hdr);
+ memcpy(&mod->klp_info->hdr, info->hdr, size);
+
+ /* Elf section header table */
+ size = sizeof(*info->sechdrs) * info->hdr->e_shnum;
+ mod->klp_info->sechdrs = kmalloc(size, GFP_KERNEL);
+ if (mod->klp_info->sechdrs == NULL) {
+ ret = -ENOMEM;
+ goto free_info;
+ }
+ memcpy(mod->klp_info->sechdrs, info->sechdrs, size);
+
+ /* Elf section name string table */
+ size = info->sechdrs[info->hdr->e_shstrndx].sh_size;
+ mod->klp_info->secstrings = kmalloc(size, GFP_KERNEL);
+ if (mod->klp_info->secstrings == NULL) {
+ ret = -ENOMEM;
+ goto free_sechdrs;
+ }
+ memcpy(mod->klp_info->secstrings, info->secstrings, size);
+
+ /* Elf symbol section index */
+ symndx = info->index.sym;
+ mod->klp_info->symndx = symndx;
+
+ /*
+ * For livepatch modules, core_kallsyms.symtab is a complete
+ * copy of the original symbol table. Adjust sh_addr to point
+ * to core_kallsyms.symtab since the copy of the symtab in module
+ * init memory is freed at the end of do_init_module().
+ */
+ mod->klp_info->sechdrs[symndx].sh_addr = \
+ (unsigned long) mod->core_kallsyms.symtab;
+
+ return 0;
+
+free_sechdrs:
+ kfree(mod->klp_info->sechdrs);
+free_info:
+ kfree(mod->klp_info);
+ return ret;
+}
+
+static void free_module_elf(struct module *mod)
+{
+ kfree(mod->klp_info->sechdrs);
+ kfree(mod->klp_info->secstrings);
+ kfree(mod->klp_info);
+}
+#else /* !CONFIG_LIVEPATCH */
+static int copy_module_elf(struct module *mod, struct load_info *info)
+{
+ return 0;
+}
+
+static void free_module_elf(struct module *mod)
+{
+}
+#endif /* CONFIG_LIVEPATCH */
+
void __weak module_memfree(void *module_region)
{
vfree(module_region);
@@ -2011,6 +2088,9 @@ static void free_module(struct module *mod)
/* Free any allocated parameters. */
destroy_params(mod->kp, mod->num_kp);
+ if (is_livepatch_module(mod))
+ free_module_elf(mod);
+
/* Now we can delete it from the lists */
mutex_lock(&module_mutex);
/* Unlink carefully: kallsyms could be walking list. */
@@ -2126,6 +2206,10 @@ static int simplify_symbols(struct module *mod, const struct load_info *info)
(long)sym[i].st_value);
break;
+ case SHN_LIVEPATCH:
+ /* Livepatch symbols are resolved by livepatch */
+ break;
+
case SHN_UNDEF:
ksym = resolve_symbol_wait(mod, info, name);
/* Ok if resolved. */
@@ -2174,6 +2258,10 @@ static int apply_relocations(struct module *mod, const struct load_info *info)
if (!(info->sechdrs[infosec].sh_flags & SHF_ALLOC))
continue;
+ /* Livepatch relocation sections are applied by livepatch */
+ if (info->sechdrs[i].sh_flags & SHF_RELA_LIVEPATCH)
+ continue;
+
if (info->sechdrs[i].sh_type == SHT_REL)
err = apply_relocate(info->sechdrs, info->strtab,
info->index.sym, i, mod);
@@ -2469,7 +2557,7 @@ static void layout_symtab(struct module *mod, struct load_info *info)
/* Compute total space required for the core symbols' strtab. */
for (ndst = i = 0; i < nsrc; i++) {
- if (i == 0 ||
+ if (i == 0 || is_livepatch_module(mod) ||
is_core_symbol(src+i, info->sechdrs, info->hdr->e_shnum,
info->index.pcpu)) {
strtab_size += strlen(&info->strtab[src[i].st_name])+1;
@@ -2528,7 +2616,7 @@ static void add_kallsyms(struct module *mod, const struct load_info *info)
mod->core_kallsyms.strtab = s = mod->core_layout.base + info->stroffs;
src = mod->kallsyms->symtab;
for (ndst = i = 0; i < mod->kallsyms->num_symtab; i++) {
- if (i == 0 ||
+ if (i == 0 || is_livepatch_module(mod) ||
is_core_symbol(src+i, info->sechdrs, info->hdr->e_shnum,
info->index.pcpu)) {
dst[ndst] = src[i];
@@ -2667,6 +2755,26 @@ static int copy_chunked_from_user(void *dst, const void __user *usrc, unsigned l
return 0;
}
+#ifdef CONFIG_LIVEPATCH
+static int find_livepatch_modinfo(struct module *mod, struct load_info *info)
+{
+ mod->klp = get_modinfo(info, "livepatch") ? true : false;
+
+ return 0;
+}
+#else /* !CONFIG_LIVEPATCH */
+static int find_livepatch_modinfo(struct module *mod, struct load_info *info)
+{
+ if (get_modinfo(info, "livepatch")) {
+ pr_err("%s: module is marked as livepatch module, but livepatch support is disabled",
+ mod->name);
+ return -ENOEXEC;
+ }
+
+ return 0;
+}
+#endif /* CONFIG_LIVEPATCH */
+
/* Sets info->hdr and info->len. */
static int copy_module_from_user(const void __user *umod, unsigned long len,
struct load_info *info)
@@ -2821,6 +2929,10 @@ static int check_modinfo(struct module *mod, struct load_info *info, int flags)
"is unknown, you have been warned.\n", mod->name);
}
+ err = find_livepatch_modinfo(mod, info);
+ if (err)
+ return err;
+
/* Set up license info based on the info section */
set_license(mod, get_modinfo(info, "license"));
@@ -3494,6 +3606,12 @@ static int load_module(struct load_info *info, const char __user *uargs,
if (err < 0)
goto coming_cleanup;
+ if (is_livepatch_module(mod)) {
+ err = copy_module_elf(mod, info);
+ if (err < 0)
+ goto sysfs_cleanup;
+ }
+
/* Get rid of temporary copy. */
free_copy(info);
@@ -3502,11 +3620,12 @@ static int load_module(struct load_info *info, const char __user *uargs,
return do_init_module(mod);
+ sysfs_cleanup:
+ mod_sysfs_teardown(mod);
coming_cleanup:
blocking_notifier_call_chain(&module_notify_list,
MODULE_STATE_GOING, mod);
klp_module_going(mod);
-
bug_cleanup:
/* module_bug_cleanup needs module_mutex protection */
mutex_lock(&module_mutex);
--
2.4.3
Livepatch needs to utilize the symbol information contained in the
mod_arch_specific struct in order to be able to call the s390
apply_relocate_add() function to apply relocations. Keep a reference to
syminfo if the module is a livepatch module. Remove the redundant vfree()
in module_finalize() since module_arch_freeing_init() (which also frees
those structures) is called in do_init_module(). If the module isn't a
livepatch module, we free the structures in module_arch_freeing_init() as
usual.
Signed-off-by: Jessica Yu <[email protected]>
Reviewed-by: Miroslav Benes <[email protected]>
---
arch/s390/kernel/module.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)
diff --git a/arch/s390/kernel/module.c b/arch/s390/kernel/module.c
index 7873e17..fbc0789 100644
--- a/arch/s390/kernel/module.c
+++ b/arch/s390/kernel/module.c
@@ -51,6 +51,10 @@ void *module_alloc(unsigned long size)
void module_arch_freeing_init(struct module *mod)
{
+ if (is_livepatch_module(mod) &&
+ mod->state == MODULE_STATE_LIVE)
+ return;
+
vfree(mod->arch.syminfo);
mod->arch.syminfo = NULL;
}
@@ -425,7 +429,5 @@ int module_finalize(const Elf_Ehdr *hdr,
struct module *me)
{
jump_label_apply_nops(me);
- vfree(me->arch.syminfo);
- me->arch.syminfo = NULL;
return 0;
}
--
2.4.3
Reuse module loader code to write relocations, thereby eliminating the need
for architecture specific relocation code in livepatch. Specifically, reuse
the apply_relocate_add() function in the module loader to write relocations
instead of duplicating functionality in livepatch's arch-dependent
klp_write_module_reloc() function.
In order to accomplish this, livepatch modules manage their own relocation
sections (marked with the SHF_RELA_LIVEPATCH section flag) and
livepatch-specific symbols (marked with SHN_LIVEPATCH symbol section
index). To apply livepatch relocation sections, livepatch symbols
referenced by relocs are resolved and then apply_relocate_add() is called
to apply those relocations.
In addition, remove x86 livepatch relocation code and the s390
klp_write_module_reloc() function stub. They are no longer needed since
relocation work has been offloaded to module loader.
Lastly, mark the module as a livepatch module so that the module loader
canappropriately identify and initialize it.
Signed-off-by: Jessica Yu <[email protected]>
Reviewed-by: Miroslav Benes <[email protected]>
---
arch/s390/include/asm/livepatch.h | 7 --
arch/x86/include/asm/livepatch.h | 2 -
arch/x86/kernel/Makefile | 1 -
arch/x86/kernel/livepatch.c | 70 -----------------
include/linux/livepatch.h | 20 -----
kernel/livepatch/core.c | 148 ++++++++++++++++++++++-------------
samples/livepatch/livepatch-sample.c | 1 +
7 files changed, 95 insertions(+), 154 deletions(-)
delete mode 100644 arch/x86/kernel/livepatch.c
diff --git a/arch/s390/include/asm/livepatch.h b/arch/s390/include/asm/livepatch.h
index d5427c7..2c12137 100644
--- a/arch/s390/include/asm/livepatch.h
+++ b/arch/s390/include/asm/livepatch.h
@@ -24,13 +24,6 @@ static inline int klp_check_compiler_support(void)
return 0;
}
-static inline int klp_write_module_reloc(struct module *mod, unsigned long
- type, unsigned long loc, unsigned long value)
-{
- /* not supported yet */
- return -ENOSYS;
-}
-
static inline void klp_arch_set_pc(struct pt_regs *regs, unsigned long ip)
{
regs->psw.addr = ip;
diff --git a/arch/x86/include/asm/livepatch.h b/arch/x86/include/asm/livepatch.h
index 7e68f95..a7f9181 100644
--- a/arch/x86/include/asm/livepatch.h
+++ b/arch/x86/include/asm/livepatch.h
@@ -32,8 +32,6 @@ static inline int klp_check_compiler_support(void)
#endif
return 0;
}
-int klp_write_module_reloc(struct module *mod, unsigned long type,
- unsigned long loc, unsigned long value);
static inline void klp_arch_set_pc(struct pt_regs *regs, unsigned long ip)
{
diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
index 616ebd2..89f8ade 100644
--- a/arch/x86/kernel/Makefile
+++ b/arch/x86/kernel/Makefile
@@ -79,7 +79,6 @@ obj-$(CONFIG_X86_MPPARSE) += mpparse.o
obj-y += apic/
obj-$(CONFIG_X86_REBOOTFIXUPS) += reboot_fixups_32.o
obj-$(CONFIG_DYNAMIC_FTRACE) += ftrace.o
-obj-$(CONFIG_LIVEPATCH) += livepatch.o
obj-$(CONFIG_FUNCTION_GRAPH_TRACER) += ftrace.o
obj-$(CONFIG_FTRACE_SYSCALLS) += ftrace.o
obj-$(CONFIG_X86_TSC) += trace_clock.o
diff --git a/arch/x86/kernel/livepatch.c b/arch/x86/kernel/livepatch.c
deleted file mode 100644
index 92fc1a5..0000000
--- a/arch/x86/kernel/livepatch.c
+++ /dev/null
@@ -1,70 +0,0 @@
-/*
- * livepatch.c - x86-specific Kernel Live Patching Core
- *
- * Copyright (C) 2014 Seth Jennings <[email protected]>
- * Copyright (C) 2014 SUSE
- *
- * This program is free software; you can redistribute it and/or
- * modify it under the terms of the GNU General Public License
- * as published by the Free Software Foundation; either version 2
- * of the License, or (at your option) any later version.
- *
- * This program is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
- * GNU General Public License for more details.
- *
- * You should have received a copy of the GNU General Public License
- * along with this program; if not, see <http://www.gnu.org/licenses/>.
- */
-
-#include <linux/module.h>
-#include <linux/uaccess.h>
-#include <asm/elf.h>
-#include <asm/livepatch.h>
-
-/**
- * klp_write_module_reloc() - write a relocation in a module
- * @mod: module in which the section to be modified is found
- * @type: ELF relocation type (see asm/elf.h)
- * @loc: address that the relocation should be written to
- * @value: relocation value (sym address + addend)
- *
- * This function writes a relocation to the specified location for
- * a particular module.
- */
-int klp_write_module_reloc(struct module *mod, unsigned long type,
- unsigned long loc, unsigned long value)
-{
- size_t size = 4;
- unsigned long val;
- unsigned long core = (unsigned long)mod->core_layout.base;
- unsigned long core_size = mod->core_layout.size;
-
- switch (type) {
- case R_X86_64_NONE:
- return 0;
- case R_X86_64_64:
- val = value;
- size = 8;
- break;
- case R_X86_64_32:
- val = (u32)value;
- break;
- case R_X86_64_32S:
- val = (s32)value;
- break;
- case R_X86_64_PC32:
- val = (u32)(value - loc);
- break;
- default:
- /* unsupported relocation type */
- return -EINVAL;
- }
-
- if (loc < core || loc >= core + core_size)
- /* loc does not point to any symbol inside the module */
- return -EINVAL;
-
- return probe_kernel_write((void *)loc, &val, size);
-}
diff --git a/include/linux/livepatch.h b/include/linux/livepatch.h
index bd830d5..0933ca4 100644
--- a/include/linux/livepatch.h
+++ b/include/linux/livepatch.h
@@ -65,27 +65,8 @@ struct klp_func {
};
/**
- * struct klp_reloc - relocation structure for live patching
- * @loc: address where the relocation will be written
- * @sympos: position in kallsyms to disambiguate symbols (optional)
- * @type: ELF relocation type
- * @name: name of the referenced symbol (for lookup/verification)
- * @addend: offset from the referenced symbol
- * @external: symbol is either exported or within the live patch module itself
- */
-struct klp_reloc {
- unsigned long loc;
- unsigned long sympos;
- unsigned long type;
- const char *name;
- int addend;
- int external;
-};
-
-/**
* struct klp_object - kernel object structure for live patching
* @name: module name (or NULL for vmlinux)
- * @relocs: relocation entries to be applied at load time
* @funcs: function entries for functions to be patched in the object
* @kobj: kobject for sysfs resources
* @mod: kernel module associated with the patched object
@@ -95,7 +76,6 @@ struct klp_reloc {
struct klp_object {
/* external */
const char *name;
- struct klp_reloc *relocs;
struct klp_func *funcs;
/* internal */
diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
index d68fbf6..eb5db6e 100644
--- a/kernel/livepatch/core.c
+++ b/kernel/livepatch/core.c
@@ -28,6 +28,8 @@
#include <linux/list.h>
#include <linux/kallsyms.h>
#include <linux/livepatch.h>
+#include <linux/elf.h>
+#include <linux/moduleloader.h>
#include <asm/cacheflush.h>
/**
@@ -204,75 +206,109 @@ static int klp_find_object_symbol(const char *objname, const char *name,
return -EINVAL;
}
-/*
- * external symbols are located outside the parent object (where the parent
- * object is either vmlinux or the kmod being patched).
- */
-static int klp_find_external_symbol(struct module *pmod, const char *name,
- unsigned long *addr)
+static int klp_resolve_symbols(Elf_Shdr *relasec, struct module *pmod)
{
- const struct kernel_symbol *sym;
-
- /* first, check if it's an exported symbol */
- preempt_disable();
- sym = find_symbol(name, NULL, NULL, true, true);
- if (sym) {
- *addr = sym->value;
- preempt_enable();
- return 0;
- }
- preempt_enable();
+ int i, cnt, vmlinux, ret;
+ char objname[MODULE_NAME_LEN];
+ char symname[KSYM_NAME_LEN];
+ char *strtab = pmod->core_kallsyms.strtab;
+ Elf_Rela *relas;
+ Elf_Sym *sym;
+ unsigned long sympos, addr;
/*
- * Check if it's in another .o within the patch module. This also
- * checks that the external symbol is unique.
+ * Since the field widths for objname and symname in the sscanf()
+ * call are hard-coded and correspond to MODULE_NAME_LEN and
+ * KSYM_NAME_LEN respectively, we must make sure that MODULE_NAME_LEN
+ * and KSYM_NAME_LEN have the values we expect them to have.
+ *
+ * Because the value of MODULE_NAME_LEN can differ among architectures,
+ * we use the smallest/strictest upper bound possible (56, based on
+ * the current definition of MODULE_NAME_LEN) to prevent overflows.
*/
- return klp_find_object_symbol(pmod->name, name, 0, addr);
+ BUILD_BUG_ON(MODULE_NAME_LEN < 56 || KSYM_NAME_LEN != 128);
+
+ relas = (Elf_Rela *) relasec->sh_addr;
+ /* For each rela in this klp relocation section */
+ for (i = 0; i < relasec->sh_size / sizeof(Elf_Rela); i++) {
+ sym = pmod->core_kallsyms.symtab + ELF_R_SYM(relas[i].r_info);
+ if (sym->st_shndx != SHN_LIVEPATCH) {
+ pr_err("symbol %s is not marked as a livepatch symbol",
+ strtab + sym->st_name);
+ return -EINVAL;
+ }
+
+ /* Format: .klp.sym.objname.symname,sympos */
+ cnt = sscanf(strtab + sym->st_name,
+ ".klp.sym.%55[^.].%127[^,],%lu",
+ objname, symname, &sympos);
+ if (cnt != 3) {
+ pr_err("symbol %s has an incorrectly formatted name",
+ strtab + sym->st_name);
+ return -EINVAL;
+ }
+
+ /* klp_find_object_symbol() treats a NULL objname as vmlinux */
+ vmlinux = !strcmp(objname, "vmlinux");
+ ret = klp_find_object_symbol(vmlinux ? NULL : objname,
+ symname, sympos, &addr);
+ if (ret)
+ return ret;
+
+ sym->st_value = addr;
+ }
+
+ return 0;
}
static int klp_write_object_relocations(struct module *pmod,
struct klp_object *obj)
{
- int ret = 0;
- unsigned long val;
- struct klp_reloc *reloc;
+ int i, cnt, ret = 0;
+ const char *objname, *secname;
+ char sec_objname[MODULE_NAME_LEN];
+ Elf_Shdr *sec;
if (WARN_ON(!klp_is_object_loaded(obj)))
return -EINVAL;
- if (WARN_ON(!obj->relocs))
- return -EINVAL;
+ objname = klp_is_module(obj) ? obj->name : "vmlinux";
module_disable_ro(pmod);
+ /* For each klp relocation section */
+ for (i = 1; i < pmod->klp_info->hdr.e_shnum; i++) {
+ sec = pmod->klp_info->sechdrs + i;
+ secname = pmod->klp_info->secstrings + sec->sh_name;
+ if (!(sec->sh_flags & SHF_RELA_LIVEPATCH))
+ continue;
- for (reloc = obj->relocs; reloc->name; reloc++) {
- /* discover the address of the referenced symbol */
- if (reloc->external) {
- if (reloc->sympos > 0) {
- pr_err("non-zero sympos for external reloc symbol '%s' is not supported\n",
- reloc->name);
- ret = -EINVAL;
- goto out;
- }
- ret = klp_find_external_symbol(pmod, reloc->name, &val);
- } else
- ret = klp_find_object_symbol(obj->name,
- reloc->name,
- reloc->sympos,
- &val);
+ /*
+ * Format: .klp.rela.sec_objname.section_name
+ * See comment in klp_resolve_symbols() for an explanation
+ * of the selected field width value.
+ */
+ cnt = sscanf(secname, ".klp.rela.%55[^.]", sec_objname);
+ if (cnt != 1) {
+ pr_err("section %s has an incorrectly formatted name",
+ secname);
+ ret = -EINVAL;
+ break;
+ }
+
+ if (strcmp(objname, sec_objname))
+ continue;
+
+ ret = klp_resolve_symbols(sec, pmod);
if (ret)
- goto out;
+ break;
- ret = klp_write_module_reloc(pmod, reloc->type, reloc->loc,
- val + reloc->addend);
- if (ret) {
- pr_err("relocation failed for symbol '%s' at 0x%016lx (%d)\n",
- reloc->name, val, ret);
- goto out;
- }
+ ret = apply_relocate_add(pmod->klp_info->sechdrs,
+ pmod->core_kallsyms.strtab,
+ pmod->klp_info->symndx, i, pmod);
+ if (ret)
+ break;
}
-out:
module_enable_ro(pmod);
return ret;
}
@@ -703,11 +739,9 @@ static int klp_init_object_loaded(struct klp_patch *patch,
struct klp_func *func;
int ret;
- if (obj->relocs) {
- ret = klp_write_object_relocations(patch->mod, obj);
- if (ret)
- return ret;
- }
+ ret = klp_write_object_relocations(patch->mod, obj);
+ if (ret)
+ return ret;
klp_for_each_func(obj, func) {
ret = klp_find_object_symbol(obj->name, func->old_name,
@@ -842,6 +876,12 @@ int klp_register_patch(struct klp_patch *patch)
{
int ret;
+ if (!is_livepatch_module(patch->mod)) {
+ pr_err("module %s is not marked as a livepatch module",
+ patch->mod->name);
+ return -EINVAL;
+ }
+
if (!klp_initialized())
return -ENODEV;
diff --git a/samples/livepatch/livepatch-sample.c b/samples/livepatch/livepatch-sample.c
index fb8c861..e34f871 100644
--- a/samples/livepatch/livepatch-sample.c
+++ b/samples/livepatch/livepatch-sample.c
@@ -89,3 +89,4 @@ static void livepatch_exit(void)
module_init(livepatch_init);
module_exit(livepatch_exit);
MODULE_LICENSE("GPL");
+MODULE_INFO(livepatch, "Y");
--
2.4.3
Document livepatch module requirements and the special Elf constants patch
modules use.
Signed-off-by: Jessica Yu <[email protected]>
Acked-by: Miroslav Benes <[email protected]>
---
Documentation/livepatch/module-elf-format.txt | 311 ++++++++++++++++++++++++++
1 file changed, 311 insertions(+)
create mode 100644 Documentation/livepatch/module-elf-format.txt
diff --git a/Documentation/livepatch/module-elf-format.txt b/Documentation/livepatch/module-elf-format.txt
new file mode 100644
index 0000000..eedbdcf
--- /dev/null
+++ b/Documentation/livepatch/module-elf-format.txt
@@ -0,0 +1,311 @@
+===========================
+Livepatch module Elf format
+===========================
+
+This document outlines the Elf format requirements that livepatch modules must follow.
+
+-----------------
+Table of Contents
+-----------------
+0. Background and motivation
+1. Livepatch modinfo field
+2. Livepatch relocation sections
+ 2.1 What are livepatch relocation sections?
+ 2.2 Livepatch relocation section format
+ 2.2.1 Required flags
+ 2.2.2 Required name format
+ 2.2.3 Example livepatch relocation section names
+ 2.2.4 Example `readelf --sections` output
+ 2.2.5 Example `readelf --relocs` output
+3. Livepatch symbols
+ 3.1 What are livepatch symbols?
+ 3.2 A livepatch module's symbol table
+ 3.3 Livepatch symbol format
+ 3.3.1 Required flags
+ 3.3.2 Required name format
+ 3.3.3 Example livepatch symbol names
+ 3.3.4 Example `readelf --symbols` output
+4. Symbol table and Elf section access
+
+----------------------------
+0. Background and motivation
+----------------------------
+
+Formerly, livepatch required separate architecture-specific code to write
+relocations. However, arch-specific code to write relocations already
+exists in the module loader, so this former approach produced redundant
+code. So, instead of duplicating code and re-implementing what the module
+loader can already do, livepatch leverages existing code in the module
+loader to perform the all the arch-specific relocation work. Specifically,
+livepatch reuses the apply_relocate_add() function in the module loader to
+write relocations. The patch module Elf format described in this document
+enables livepatch to be able to do this. The hope is that this will make
+livepatch more easily portable to other architectures and reduce the amount
+of arch-specific code required to port livepatch to a particular
+architecture.
+
+Since apply_relocate_add() requires access to a module's section header
+table, symbol table, and relocation section indices, Elf information is
+preserved for livepatch modules (see section 4). Livepatch manages its own
+relocation sections and symbols, which are described in this document. The
+Elf constants used to mark livepatch symbols and relocation sections were
+selected from OS-specific ranges according to the definitions from glibc.
+
+0.1 Why does livepatch need to write its own relocations?
+---------------------------------------------------------
+A typical livepatch module contains patched versions of functions that can
+reference non-exported global symbols and non-included local symbols.
+Relocations referencing these types of symbols cannot be left in as-is
+since the kernel module loader cannot resolve them and will therefore
+reject the livepatch module. Furthermore, we cannot apply relocations that
+affect modules not yet loaded at patch module load time (e.g. a patch to a
+driver that is not loaded). Formerly, livepatch solved this problem by
+embedding special "dynrela" (dynamic rela) sections in the resulting patch
+module Elf output. Using these dynrela sections, livepatch could resolve
+symbols while taking into account its scope and what module the symbol
+belongs to, and then manually apply the dynamic relocations. However this
+approach required livepatch to supply arch-specific code in order to write
+these relocations. In the new format, livepatch manages its own SHT_RELA
+relocation sections in place of dynrela sections, and the symbols that the
+relas reference are special livepatch symbols (see section 2 and 3). The
+arch-specific livepatch relocation code is replaced by a call to
+apply_relocate_add().
+
+================================
+PATCH MODULE FORMAT REQUIREMENTS
+================================
+
+--------------------------
+1. Livepatch modinfo field
+--------------------------
+
+Livepatch modules are required to have the "livepatch" modinfo attribute.
+See the sample livepatch module in samples/livepatch/ for how this is done.
+
+Livepatch modules can be identified by users by using the 'modinfo' command
+and looking for the presence of the "livepatch" field. This field is also
+used by the kernel module loader to identify livepatch modules.
+
+Example modinfo output:
+-----------------------
+% modinfo livepatch-meminfo.ko
+filename: livepatch-meminfo.ko
+livepatch: Y
+license: GPL
+depends:
+vermagic: 4.3.0+ SMP mod_unload
+
+--------------------------------
+2. Livepatch relocation sections
+--------------------------------
+
+-------------------------------------------
+2.1 What are livepatch relocation sections?
+-------------------------------------------
+A livepatch module manages its own Elf relocation sections to apply
+relocations to modules as well as to the kernel (vmlinux) at the
+appropriate time. For example, if a patch module patches a driver that is
+not currently loaded, livepatch will apply the corresponding livepatch
+relocation section(s) to the driver once it loads.
+
+Each "object" (e.g. vmlinux, or a module) within a patch module may have
+multiple livepatch relocation sections associated with it (e.g. patches to
+multiple functions within the same object). There is a 1-1 correspondence
+between a livepatch relocation section and the target section (usually the
+text section of a function) to which the relocation(s) apply. It is
+also possible for a livepatch module to have no livepatch relocation
+sections, as in the case of the sample livepatch module (see
+samples/livepatch).
+
+Since Elf information is preserved for livepatch modules (see Section 4), a
+livepatch relocation section can be applied simply by passing in the
+appropriate section index to apply_relocate_add(), which then uses it to
+access the relocation section and apply the relocations.
+
+Every symbol referenced by a rela in a livepatch relocation section is a
+livepatch symbol. These must be resolved before livepatch can call
+apply_relocate_add(). See Section 3 for more information.
+
+---------------------------------------
+2.2 Livepatch relocation section format
+---------------------------------------
+
+2.2.1 Required flags
+--------------------
+Livepatch relocation sections must be marked with the SHF_RELA_LIVEPATCH
+section flag. See include/uapi/linux/elf.h for the definition. The module
+loader recognizes this flag and will avoid applying those relocation sections
+at patch module load time. These sections must also be marked with SHF_ALLOC,
+so that the module loader doesn't discard them on module load (i.e. they will
+be copied into memory along with the other SHF_ALLOC sections).
+
+2.2.2 Required name format
+--------------------------
+The name of a livepatch relocation section must conform to the following format:
+
+.klp.rela.objname.section_name
+^ ^^ ^ ^ ^
+|________||_____| |__________|
+ [A] [B] [C]
+
+[A] The relocation section name is prefixed with the string ".klp.rela."
+[B] The name of the object (i.e. "vmlinux" or name of module) to
+ which the relocation section belongs follows immediately after the prefix.
+[C] The actual name of the section to which this relocation section applies.
+
+2.2.3 Example livepatch relocation section names:
+-------------------------------------------------
+.klp.rela.ext4.text.ext4_attr_store
+.klp.rela.vmlinux.text.cmdline_proc_show
+
+2.2.4 Example `readelf --sections` output for a patch
+module that patches vmlinux and modules 9p, btrfs, ext4:
+--------------------------------------------------------
+ Section Headers:
+ [Nr] Name Type Address Off Size ES Flg Lk Inf Al
+ [ snip ]
+ [29] .klp.rela.9p.text.caches.show RELA 0000000000000000 002d58 0000c0 18 AIo 64 9 8
+ [30] .klp.rela.btrfs.text.btrfs.feature.attr.show RELA 0000000000000000 002e18 000060 18 AIo 64 11 8
+ [ snip ]
+ [34] .klp.rela.ext4.text.ext4.attr.store RELA 0000000000000000 002fd8 0000d8 18 AIo 64 13 8
+ [35] .klp.rela.ext4.text.ext4.attr.show RELA 0000000000000000 0030b0 000150 18 AIo 64 15 8
+ [36] .klp.rela.vmlinux.text.cmdline.proc.show RELA 0000000000000000 003200 000018 18 AIo 64 17 8
+ [37] .klp.rela.vmlinux.text.meminfo.proc.show RELA 0000000000000000 003218 0000f0 18 AIo 64 19 8
+ [ snip ] ^ ^
+ | |
+ [*] [*]
+[*] Livepatch relocation sections are SHT_RELA sections but with a few special
+characteristics. Notice that they are marked SHF_ALLOC ("A") so that they will
+not be discarded when the module is loaded into memory, as well as with the
+SHF_RELA_LIVEPATCH flag ("o" - for OS-specific).
+
+2.2.5 Example `readelf --relocs` output for a patch module:
+-----------------------------------------------------------
+Relocation section '.klp.rela.btrfs.text.btrfs_feature_attr_show' at offset 0x2ba0 contains 4 entries:
+ Offset Info Type Symbol's Value Symbol's Name + Addend
+000000000000001f 0000005e00000002 R_X86_64_PC32 0000000000000000 .klp.sym.vmlinux.printk,0 - 4
+0000000000000028 0000003d0000000b R_X86_64_32S 0000000000000000 .klp.sym.btrfs.btrfs_ktype,0 + 0
+0000000000000036 0000003b00000002 R_X86_64_PC32 0000000000000000 .klp.sym.btrfs.can_modify_feature.isra.3,0 - 4
+000000000000004c 0000004900000002 R_X86_64_PC32 0000000000000000 .klp.sym.vmlinux.snprintf,0 - 4
+[ snip ] ^
+ |
+ [*]
+[*] Every symbol referenced by a relocation is a livepatch symbol.
+
+--------------------
+3. Livepatch symbols
+--------------------
+
+-------------------------------
+3.1 What are livepatch symbols?
+-------------------------------
+Livepatch symbols are symbols referred to by livepatch relocation sections.
+These are symbols accessed from new versions of functions for patched
+objects, whose addresses cannot be resolved by the module loader (because
+they are local or unexported global syms). Since the module loader only
+resolves exported syms, and not every symbol referenced by the new patched
+functions is exported, livepatch symbols were introduced. They are used
+also in cases where we cannot immediately know the address of a symbol when
+a patch module loads. For example, this is the case when livepatch patches
+a module that is not loaded yet. In this case, the relevant livepatch
+symbols are resolved simply when the target module loads. In any case, for
+any livepatch relocation section, all livepatch symbols referenced by that
+section must be resolved before livepatch can call apply_relocate_add() for
+that reloc section.
+
+Livepatch symbols must be marked with SHN_LIVEPATCH so that the module
+loader can identify and ignore them. Livepatch modules keep these symbols
+in their symbol tables, and the symbol table is made accessible through
+module->symtab.
+
+-------------------------------------
+3.2 A livepatch module's symbol table
+-------------------------------------
+Normally, a stripped down copy of a module's symbol table (containing only
+"core" symbols) is made available through module->symtab (See layout_symtab()
+in kernel/module.c). For livepatch modules, the symbol table copied into memory
+on module load must be exactly the same as the symbol table produced when the
+patch module was compiled. This is because the relocations in each livepatch
+relocation section refer to their respective symbols with their symbol indices,
+and the original symbol indices (and thus the symtab ordering) must be
+preserved in order for apply_relocate_add() to find the right symbol.
+
+For example, take this particular rela from a livepatch module:
+Relocation section '.klp.rela.btrfs.text.btrfs_feature_attr_show' at offset 0x2ba0 contains 4 entries:
+ Offset Info Type Symbol's Value Symbol's Name + Addend
+000000000000001f 0000005e00000002 R_X86_64_PC32 0000000000000000 .klp.sym.vmlinux.printk,0 - 4
+
+This rela refers to the symbol '.klp.sym.vmlinux.printk,0', and the symbol index is encoded
+in 'Info'. Here its symbol index is 0x5e, which is 94 in decimal, which refers to the
+symbol index 94.
+And in this patch module's corresponding symbol table, symbol index 94 refers to that very symbol:
+[ snip ]
+94: 0000000000000000 0 NOTYPE GLOBAL DEFAULT OS [0xff20] .klp.sym.vmlinux.printk,0
+[ snip ]
+
+---------------------------
+3.3 Livepatch symbol format
+---------------------------
+
+3.3.1 Required flags
+--------------------
+Livepatch symbols must have their section index marked as SHN_LIVEPATCH, so
+that the module loader can identify them and not attempt to resolve them.
+See include/uapi/linux/elf.h for the actual definitions.
+
+3.3.2 Required name format
+--------------------------
+Livepatch symbol names must conform to the following format:
+
+.klp.sym.objname.symbol_name,sympos
+^ ^^ ^ ^ ^ ^
+|_______||_____| |_________| |
+ [A] [B] [C] [D]
+
+[A] The symbol name is prefixed with the string ".klp.sym."
+[B] The name of the object (i.e. "vmlinux" or name of module) to
+ which the symbol belongs follows immediately after the prefix.
+[C] The actual name of the symbol.
+[D] The position of the symbol in the object (as according to kallsyms)
+ This is used to differentiate duplicate symbols within the same
+ object. The symbol position is expressed numerically (0, 1, 2...).
+ The symbol position of a unique symbol is 0.
+
+3.3.3 Example livepatch symbol names:
+-------------------------------------
+.klp.sym.vmlinux.snprintf,0
+.klp.sym.vmlinux.printk,0
+.klp.sym.btrfs.btrfs_ktype,0
+
+3.3.4 Example `readelf --symbols` output for a patch module:
+------------------------------------------------------------
+Symbol table '.symtab' contains 127 entries:
+ Num: Value Size Type Bind Vis Ndx Name
+ [ snip ]
+ 73: 0000000000000000 0 NOTYPE GLOBAL DEFAULT OS [0xff20] .klp.sym.vmlinux.snprintf,0
+ 74: 0000000000000000 0 NOTYPE GLOBAL DEFAULT OS [0xff20] .klp.sym.vmlinux.capable,0
+ 75: 0000000000000000 0 NOTYPE GLOBAL DEFAULT OS [0xff20] .klp.sym.vmlinux.find_next_bit,0
+ 76: 0000000000000000 0 NOTYPE GLOBAL DEFAULT OS [0xff20] .klp.sym.vmlinux.si_swapinfo,0
+ [ snip ] ^
+ |
+ [*]
+[*] Note that the 'Ndx' (Section index) for these symbols is SHN_LIVEPATCH (0xff20).
+ "OS" means OS-specific.
+
+--------------------------------------
+4. Symbol table and Elf section access
+--------------------------------------
+A livepatch module's symbol table is accessible through module->symtab.
+
+Since apply_relocate_add() requires access to a module's section headers,
+symbol table, and relocation section indices, Elf information is preserved for
+livepatch modules and is made accessible by the module loader through
+module->klp_info, which is a klp_modinfo struct. When a livepatch module loads,
+this struct is filled in by the module loader. Its fields are documented below:
+
+struct klp_modinfo {
+ Elf_Ehdr hdr; /* Elf header */
+ Elf_Shdr *sechdrs; /* Section header table */
+ char *secstrings; /* String table for the section headers */
+ unsigned int symndx; /* The symbol table section index */
+};
--
2.4.3
On Tue, Mar 22, 2016 at 08:03:14PM -0400, Jessica Yu wrote:
> Patches based on linux-next.
>
> Previous patchset (v5) found here:
> http://lkml.kernel.org/g/[email protected]
>
> v6:
> - Since we hard-code the field widths for the objname and symbol name
> for the sscanf() calls, which are supposed to correspond to the values
> of MODULE_NAME_LEN and KSYM_NAME_LEN, use BUILD_BUG_ON() to detect when
> the values of these constants deviate from the expected values.
> - Squash the sample livepatch module patch into patch 4
> ("livepatch: reuse module loader code to write relocations") so
> git bisects don't break
> - Don't need the klp_buf struct, just use plain char arrays to hold the
> output of sscanf(). Also, no need to clear the bufs after every
> invocation, as sscanf() takes care to put a null byte at the end of
> the bufs.
> - Fix compiler kbuild errors for the !CONFIG_LIVEPATCH case
> - Fixed some small module.c nits
For the series:
Acked-by: Josh Poimboeuf <[email protected]>
Thanks Jessica!
--
Josh
On Tue, 22 Mar 2016, Jessica Yu wrote:
> v6:
> - Since we hard-code the field widths for the objname and symbol name
> for the sscanf() calls, which are supposed to correspond to the values
> of MODULE_NAME_LEN and KSYM_NAME_LEN, use BUILD_BUG_ON() to detect when
> the values of these constants deviate from the expected values.
> - Squash the sample livepatch module patch into patch 4
> ("livepatch: reuse module loader code to write relocations") so
> git bisects don't break
> - Don't need the klp_buf struct, just use plain char arrays to hold the
> output of sscanf(). Also, no need to clear the bufs after every
> invocation, as sscanf() takes care to put a null byte at the end of
> the bufs.
> - Fix compiler kbuild errors for the !CONFIG_LIVEPATCH case
> - Fixed some small module.c nits
FWIW I am fine with all the changes and my Reviewed-by tag is still valid.
Great job, Jessica.
Miroslav
+++ Jessica Yu [22/03/16 20:03 -0400]:
>
>Patches based on linux-next.
>
>Previous patchset (v5) found here:
>http://lkml.kernel.org/g/[email protected]
>
>v6:
> - Since we hard-code the field widths for the objname and symbol name
> for the sscanf() calls, which are supposed to correspond to the values
> of MODULE_NAME_LEN and KSYM_NAME_LEN, use BUILD_BUG_ON() to detect when
> the values of these constants deviate from the expected values.
> - Squash the sample livepatch module patch into patch 4
> ("livepatch: reuse module loader code to write relocations") so
> git bisects don't break
> - Don't need the klp_buf struct, just use plain char arrays to hold the
> output of sscanf(). Also, no need to clear the bufs after every
> invocation, as sscanf() takes care to put a null byte at the end of
> the bufs.
> - Fix compiler kbuild errors for the !CONFIG_LIVEPATCH case
> - Fixed some small module.c nits
>
Pinging Rusty, just in case this thread got buried :-)
How do the module.c changes look?
Thanks,
Jessica
On Tue, 29 Mar 2016, Jessica Yu wrote:
> > v6:
> > - Since we hard-code the field widths for the objname and symbol name
> > for the sscanf() calls, which are supposed to correspond to the values
> > of MODULE_NAME_LEN and KSYM_NAME_LEN, use BUILD_BUG_ON() to detect when
> > the values of these constants deviate from the expected values.
> > - Squash the sample livepatch module patch into patch 4
> > ("livepatch: reuse module loader code to write relocations") so
> > git bisects don't break
> > - Don't need the klp_buf struct, just use plain char arrays to hold the
> > output of sscanf(). Also, no need to clear the bufs after every
> > invocation, as sscanf() takes care to put a null byte at the end of
> > the bufs.
> > - Fix compiler kbuild errors for the !CONFIG_LIVEPATCH case
> > - Fixed some small module.c nits
> >
>
> Pinging Rusty, just in case this thread got buried :-)
> How do the module.c changes look?
Plus there are (admittedly indeed rather small and trivial) changes to
s390 module loader, so I'd prefer to have Heiko's / Martin's Ack before
merging this.
Hence, let me piggy back on this ping to Rusty, and let me ping Heiko and
Martin as well (adding to CC explicitly to make sure this doesn't get lost
in general noise).
Thanks,
--
Jiri Kosina
SUSE Labs
On Wed, Mar 30, 2016 at 01:24:08AM +0200, Jiri Kosina wrote:
> On Tue, 29 Mar 2016, Jessica Yu wrote:
>
> > > v6:
> > > - Since we hard-code the field widths for the objname and symbol name
> > > for the sscanf() calls, which are supposed to correspond to the values
> > > of MODULE_NAME_LEN and KSYM_NAME_LEN, use BUILD_BUG_ON() to detect when
> > > the values of these constants deviate from the expected values.
> > > - Squash the sample livepatch module patch into patch 4
> > > ("livepatch: reuse module loader code to write relocations") so
> > > git bisects don't break
> > > - Don't need the klp_buf struct, just use plain char arrays to hold the
> > > output of sscanf(). Also, no need to clear the bufs after every
> > > invocation, as sscanf() takes care to put a null byte at the end of
> > > the bufs.
> > > - Fix compiler kbuild errors for the !CONFIG_LIVEPATCH case
> > > - Fixed some small module.c nits
> > >
> >
> > Pinging Rusty, just in case this thread got buried :-)
> > How do the module.c changes look?
>
> Plus there are (admittedly indeed rather small and trivial) changes to
> s390 module loader, so I'd prefer to have Heiko's / Martin's Ack before
> merging this.
>
> Hence, let me piggy back on this ping to Rusty, and let me ping Heiko and
> Martin as well (adding to CC explicitly to make sure this doesn't get lost
> in general noise).
For the s390 changes:
Acked-by: Heiko Carstens <[email protected]>
Jessica, thanks for also writing the documentation!
Jessica Yu <[email protected]> writes:
> For livepatch modules, copy Elf section, symbol, and string information
> from the load_info struct in the module loader. Persist copies of the
> original symbol table and string table.
>
> Livepatch manages its own relocation sections in order to reuse module
> loader code to write relocations. Livepatch modules must preserve Elf
> information such as section indices in order to apply livepatch relocation
> sections using the module loader's apply_relocate_add() function.
>
> In order to apply livepatch relocation sections, livepatch modules must
> keep a complete copy of their original symbol table in memory. Normally, a
> stripped down copy of a module's symbol table (containing only "core"
> symbols) is made available through module->core_symtab. But for livepatch
> modules, the symbol table copied into memory on module load must be exactly
> the same as the symbol table produced when the patch module was compiled.
> This is because the relocations in each livepatch relocation section refer
> to their respective symbols with their symbol indices, and the original
> symbol indices (and thus the symtab ordering) must be preserved in order
> for apply_relocate_add() to find the right symbol.
>
> Signed-off-by: Jessica Yu <[email protected]>
> Reviewed-by: Miroslav Benes <[email protected]>
> ---
> include/linux/module.h | 25 ++++++++++
> kernel/module.c | 125 +++++++++++++++++++++++++++++++++++++++++++++++--
> 2 files changed, 147 insertions(+), 3 deletions(-)
Acked-by: Rusty Russell <[email protected]>
(I guess that takes precedence over "Reviewed-by", which I did too).
Thanks,
Rusty.
> diff --git a/include/linux/module.h b/include/linux/module.h
> index 2bb0c30..3daf2b3 100644
> --- a/include/linux/module.h
> +++ b/include/linux/module.h
> @@ -330,6 +330,15 @@ struct mod_kallsyms {
> char *strtab;
> };
>
> +#ifdef CONFIG_LIVEPATCH
> +struct klp_modinfo {
> + Elf_Ehdr hdr;
> + Elf_Shdr *sechdrs;
> + char *secstrings;
> + unsigned int symndx;
> +};
> +#endif
> +
> struct module {
> enum module_state state;
>
> @@ -456,7 +465,11 @@ struct module {
> #endif
>
> #ifdef CONFIG_LIVEPATCH
> + bool klp; /* Is this a livepatch module? */
> bool klp_alive;
> +
> + /* Elf information */
> + struct klp_modinfo *klp_info;
> #endif
>
> #ifdef CONFIG_MODULE_UNLOAD
> @@ -630,6 +643,18 @@ static inline bool module_requested_async_probing(struct module *module)
> return module && module->async_probe_requested;
> }
>
> +#ifdef CONFIG_LIVEPATCH
> +static inline bool is_livepatch_module(struct module *mod)
> +{
> + return mod->klp;
> +}
> +#else /* !CONFIG_LIVEPATCH */
> +static inline bool is_livepatch_module(struct module *mod)
> +{
> + return false;
> +}
> +#endif /* CONFIG_LIVEPATCH */
> +
> #else /* !CONFIG_MODULES... */
>
> /* Given an address, look for it in the exception tables. */
> diff --git a/kernel/module.c b/kernel/module.c
> index 041200c..5f71aa6 100644
> --- a/kernel/module.c
> +++ b/kernel/module.c
> @@ -1973,6 +1973,83 @@ static void module_enable_nx(const struct module *mod) { }
> static void module_disable_nx(const struct module *mod) { }
> #endif
>
> +#ifdef CONFIG_LIVEPATCH
> +/*
> + * Persist Elf information about a module. Copy the Elf header,
> + * section header table, section string table, and symtab section
> + * index from info to mod->klp_info.
> + */
> +static int copy_module_elf(struct module *mod, struct load_info *info)
> +{
> + unsigned int size, symndx;
> + int ret;
> +
> + size = sizeof(*mod->klp_info);
> + mod->klp_info = kmalloc(size, GFP_KERNEL);
> + if (mod->klp_info == NULL)
> + return -ENOMEM;
> +
> + /* Elf header */
> + size = sizeof(mod->klp_info->hdr);
> + memcpy(&mod->klp_info->hdr, info->hdr, size);
> +
> + /* Elf section header table */
> + size = sizeof(*info->sechdrs) * info->hdr->e_shnum;
> + mod->klp_info->sechdrs = kmalloc(size, GFP_KERNEL);
> + if (mod->klp_info->sechdrs == NULL) {
> + ret = -ENOMEM;
> + goto free_info;
> + }
> + memcpy(mod->klp_info->sechdrs, info->sechdrs, size);
> +
> + /* Elf section name string table */
> + size = info->sechdrs[info->hdr->e_shstrndx].sh_size;
> + mod->klp_info->secstrings = kmalloc(size, GFP_KERNEL);
> + if (mod->klp_info->secstrings == NULL) {
> + ret = -ENOMEM;
> + goto free_sechdrs;
> + }
> + memcpy(mod->klp_info->secstrings, info->secstrings, size);
> +
> + /* Elf symbol section index */
> + symndx = info->index.sym;
> + mod->klp_info->symndx = symndx;
> +
> + /*
> + * For livepatch modules, core_kallsyms.symtab is a complete
> + * copy of the original symbol table. Adjust sh_addr to point
> + * to core_kallsyms.symtab since the copy of the symtab in module
> + * init memory is freed at the end of do_init_module().
> + */
> + mod->klp_info->sechdrs[symndx].sh_addr = \
> + (unsigned long) mod->core_kallsyms.symtab;
> +
> + return 0;
> +
> +free_sechdrs:
> + kfree(mod->klp_info->sechdrs);
> +free_info:
> + kfree(mod->klp_info);
> + return ret;
> +}
> +
> +static void free_module_elf(struct module *mod)
> +{
> + kfree(mod->klp_info->sechdrs);
> + kfree(mod->klp_info->secstrings);
> + kfree(mod->klp_info);
> +}
> +#else /* !CONFIG_LIVEPATCH */
> +static int copy_module_elf(struct module *mod, struct load_info *info)
> +{
> + return 0;
> +}
> +
> +static void free_module_elf(struct module *mod)
> +{
> +}
> +#endif /* CONFIG_LIVEPATCH */
> +
> void __weak module_memfree(void *module_region)
> {
> vfree(module_region);
> @@ -2011,6 +2088,9 @@ static void free_module(struct module *mod)
> /* Free any allocated parameters. */
> destroy_params(mod->kp, mod->num_kp);
>
> + if (is_livepatch_module(mod))
> + free_module_elf(mod);
> +
> /* Now we can delete it from the lists */
> mutex_lock(&module_mutex);
> /* Unlink carefully: kallsyms could be walking list. */
> @@ -2126,6 +2206,10 @@ static int simplify_symbols(struct module *mod, const struct load_info *info)
> (long)sym[i].st_value);
> break;
>
> + case SHN_LIVEPATCH:
> + /* Livepatch symbols are resolved by livepatch */
> + break;
> +
> case SHN_UNDEF:
> ksym = resolve_symbol_wait(mod, info, name);
> /* Ok if resolved. */
> @@ -2174,6 +2258,10 @@ static int apply_relocations(struct module *mod, const struct load_info *info)
> if (!(info->sechdrs[infosec].sh_flags & SHF_ALLOC))
> continue;
>
> + /* Livepatch relocation sections are applied by livepatch */
> + if (info->sechdrs[i].sh_flags & SHF_RELA_LIVEPATCH)
> + continue;
> +
> if (info->sechdrs[i].sh_type == SHT_REL)
> err = apply_relocate(info->sechdrs, info->strtab,
> info->index.sym, i, mod);
> @@ -2469,7 +2557,7 @@ static void layout_symtab(struct module *mod, struct load_info *info)
>
> /* Compute total space required for the core symbols' strtab. */
> for (ndst = i = 0; i < nsrc; i++) {
> - if (i == 0 ||
> + if (i == 0 || is_livepatch_module(mod) ||
> is_core_symbol(src+i, info->sechdrs, info->hdr->e_shnum,
> info->index.pcpu)) {
> strtab_size += strlen(&info->strtab[src[i].st_name])+1;
> @@ -2528,7 +2616,7 @@ static void add_kallsyms(struct module *mod, const struct load_info *info)
> mod->core_kallsyms.strtab = s = mod->core_layout.base + info->stroffs;
> src = mod->kallsyms->symtab;
> for (ndst = i = 0; i < mod->kallsyms->num_symtab; i++) {
> - if (i == 0 ||
> + if (i == 0 || is_livepatch_module(mod) ||
> is_core_symbol(src+i, info->sechdrs, info->hdr->e_shnum,
> info->index.pcpu)) {
> dst[ndst] = src[i];
> @@ -2667,6 +2755,26 @@ static int copy_chunked_from_user(void *dst, const void __user *usrc, unsigned l
> return 0;
> }
>
> +#ifdef CONFIG_LIVEPATCH
> +static int find_livepatch_modinfo(struct module *mod, struct load_info *info)
> +{
> + mod->klp = get_modinfo(info, "livepatch") ? true : false;
> +
> + return 0;
> +}
> +#else /* !CONFIG_LIVEPATCH */
> +static int find_livepatch_modinfo(struct module *mod, struct load_info *info)
> +{
> + if (get_modinfo(info, "livepatch")) {
> + pr_err("%s: module is marked as livepatch module, but livepatch support is disabled",
> + mod->name);
> + return -ENOEXEC;
> + }
> +
> + return 0;
> +}
> +#endif /* CONFIG_LIVEPATCH */
> +
> /* Sets info->hdr and info->len. */
> static int copy_module_from_user(const void __user *umod, unsigned long len,
> struct load_info *info)
> @@ -2821,6 +2929,10 @@ static int check_modinfo(struct module *mod, struct load_info *info, int flags)
> "is unknown, you have been warned.\n", mod->name);
> }
>
> + err = find_livepatch_modinfo(mod, info);
> + if (err)
> + return err;
> +
> /* Set up license info based on the info section */
> set_license(mod, get_modinfo(info, "license"));
>
> @@ -3494,6 +3606,12 @@ static int load_module(struct load_info *info, const char __user *uargs,
> if (err < 0)
> goto coming_cleanup;
>
> + if (is_livepatch_module(mod)) {
> + err = copy_module_elf(mod, info);
> + if (err < 0)
> + goto sysfs_cleanup;
> + }
> +
> /* Get rid of temporary copy. */
> free_copy(info);
>
> @@ -3502,11 +3620,12 @@ static int load_module(struct load_info *info, const char __user *uargs,
>
> return do_init_module(mod);
>
> + sysfs_cleanup:
> + mod_sysfs_teardown(mod);
> coming_cleanup:
> blocking_notifier_call_chain(&module_notify_list,
> MODULE_STATE_GOING, mod);
> klp_module_going(mod);
> -
> bug_cleanup:
> /* module_bug_cleanup needs module_mutex protection */
> mutex_lock(&module_mutex);
> --
> 2.4.3
On Tue, 22 Mar 2016, Jessica Yu wrote:
> This patchset removes livepatch's need for architecture-specific relocation
> code by leveraging existing code in the module loader to perform
> arch-dependent work.
This is now in livepatching.git#for-4.7/arch-independent-klp-relocations
I was waiting a bit whether there would be any discussion regarding the
new relocation flag and symbol section index added to elf, but given the
fact that noone objected and that we are using the OS-specific range
anyway, I don't expect this to be an issue.
Thanks everybody,
--
Jiri Kosina
SUSE Labs