The following commit has been merged into the x86/urgent branch of tip:
Commit-ID: 4009a4ac82dd95b8cd2b62bd30019476983f0aff
Gitweb: https://git.kernel.org/tip/4009a4ac82dd95b8cd2b62bd30019476983f0aff
Author: Joerg Roedel <[email protected]>
AuthorDate: Mon, 21 Mar 2022 10:33:51 +01:00
Committer: Borislav Petkov <[email protected]>
CommitterDate: Tue, 29 Mar 2022 15:59:16 +02:00
x86/sev: Unroll string mmio with CC_ATTR_GUEST_UNROLL_STRING_IO
The io-specific memcpy/memset functions use string mmio accesses to do
their work. Under SEV, the hypervisor can't emulate these instructions
because they read/write directly from/to encrypted memory.
KVM will inject a page fault exception into the guest when it is asked
to emulate string mmio instructions for an SEV guest:
BUG: unable to handle page fault for address: ffffc90000065068
#PF: supervisor read access in kernel mode
#PF: error_code(0x0000) - not-present page
PGD 8000100000067 P4D 8000100000067 PUD 80001000fb067 PMD 80001000fc067 PTE 80000000fed40173
Oops: 0000 [#1] PREEMPT SMP NOPTI
CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.17.0-rc7 #3
As string mmio for an SEV guest can not be supported by the
hypervisor, unroll the instructions for CC_ATTR_GUEST_UNROLL_STRING_IO
enabled kernels.
This issue appears when kernels are launched in recent libvirt-managed
SEV virtual machines, because virt-install started to add a tpm-crb
device to the guest by default and proactively because, raisins:
https://github.com/virt-manager/virt-manager/commit/eb58c09f488b0633ed1eea012cd311e48864401e
and as that commit says, the default adding of a TPM can be disabled
with "virt-install ... --tpm none".
The kernel driver for tpm-crb uses memcpy_to/from_io() functions to
access MMIO memory, resulting in a page-fault injected by KVM and
crashing the kernel at boot.
[ bp: Massage and extend commit message. ]
Fixes: d8aa7eea78a1 ('x86/mm: Add Secure Encrypted Virtualization (SEV) support')
Signed-off-by: Joerg Roedel <[email protected]>
Signed-off-by: Borislav Petkov <[email protected]>
Reviewed-by: Tom Lendacky <[email protected]>
Cc: <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
---
arch/x86/lib/iomem.c | 65 +++++++++++++++++++++++++++++++++++++------
1 file changed, 57 insertions(+), 8 deletions(-)
diff --git a/arch/x86/lib/iomem.c b/arch/x86/lib/iomem.c
index df50451..3e2f33f 100644
--- a/arch/x86/lib/iomem.c
+++ b/arch/x86/lib/iomem.c
@@ -22,7 +22,7 @@ static __always_inline void rep_movs(void *to, const void *from, size_t n)
: "memory");
}
-void memcpy_fromio(void *to, const volatile void __iomem *from, size_t n)
+static void string_memcpy_fromio(void *to, const volatile void __iomem *from, size_t n)
{
if (unlikely(!n))
return;
@@ -38,9 +38,8 @@ void memcpy_fromio(void *to, const volatile void __iomem *from, size_t n)
}
rep_movs(to, (const void *)from, n);
}
-EXPORT_SYMBOL(memcpy_fromio);
-void memcpy_toio(volatile void __iomem *to, const void *from, size_t n)
+static void string_memcpy_toio(volatile void __iomem *to, const void *from, size_t n)
{
if (unlikely(!n))
return;
@@ -56,14 +55,64 @@ void memcpy_toio(volatile void __iomem *to, const void *from, size_t n)
}
rep_movs((void *)to, (const void *) from, n);
}
+
+static void unrolled_memcpy_fromio(void *to, const volatile void __iomem *from, size_t n)
+{
+ const volatile char __iomem *in = from;
+ char *out = to;
+ int i;
+
+ for (i = 0; i < n; ++i)
+ out[i] = readb(&in[i]);
+}
+
+static void unrolled_memcpy_toio(volatile void __iomem *to, const void *from, size_t n)
+{
+ volatile char __iomem *out = to;
+ const char *in = from;
+ int i;
+
+ for (i = 0; i < n; ++i)
+ writeb(in[i], &out[i]);
+}
+
+static void unrolled_memset_io(volatile void __iomem *a, int b, size_t c)
+{
+ volatile char __iomem *mem = a;
+ int i;
+
+ for (i = 0; i < c; ++i)
+ writeb(b, &mem[i]);
+}
+
+void memcpy_fromio(void *to, const volatile void __iomem *from, size_t n)
+{
+ if (cc_platform_has(CC_ATTR_GUEST_UNROLL_STRING_IO))
+ unrolled_memcpy_fromio(to, from, n);
+ else
+ string_memcpy_fromio(to, from, n);
+}
+EXPORT_SYMBOL(memcpy_fromio);
+
+void memcpy_toio(volatile void __iomem *to, const void *from, size_t n)
+{
+ if (cc_platform_has(CC_ATTR_GUEST_UNROLL_STRING_IO))
+ unrolled_memcpy_toio(to, from, n);
+ else
+ string_memcpy_toio(to, from, n);
+}
EXPORT_SYMBOL(memcpy_toio);
void memset_io(volatile void __iomem *a, int b, size_t c)
{
- /*
- * TODO: memset can mangle the IO patterns quite a bit.
- * perhaps it would be better to use a dumb one:
- */
- memset((void *)a, b, c);
+ if (cc_platform_has(CC_ATTR_GUEST_UNROLL_STRING_IO)) {
+ unrolled_memset_io(a, b, c);
+ } else {
+ /*
+ * TODO: memset can mangle the IO patterns quite a bit.
+ * perhaps it would be better to use a dumb one:
+ */
+ memset((void *)a, b, c);
+ }
}
EXPORT_SYMBOL(memset_io);
Isn't this patch entirely broken?
Even the 'normal' kernel functions are broken.
memcpy_toio() and memcpy_fromio() need to be using 64bit
accesses to IO space.
They used to be implemented using memcpy() - but that can end
up being 'rep movsb' which is always byte copies on uncached
memory.
I thought that had been fixed to used a better copy loop.
David
> -----Original Message-----
> From: [email protected] <[email protected]>
> Sent: 29 March 2022 15:39
> To: [email protected]
> Cc: Joerg Roedel <[email protected]>; Borislav Petkov <[email protected]>; Tom Lendacky
> <[email protected]>; [email protected]; [email protected]; [email protected]
> Subject: [tip: x86/urgent] x86/sev: Unroll string mmio with CC_ATTR_GUEST_UNROLL_STRING_IO
>
> The following commit has been merged into the x86/urgent branch of tip:
>
> Commit-ID: 4009a4ac82dd95b8cd2b62bd30019476983f0aff
> Gitweb: https://git.kernel.org/tip/4009a4ac82dd95b8cd2b62bd30019476983f0aff
> Author: Joerg Roedel <[email protected]>
> AuthorDate: Mon, 21 Mar 2022 10:33:51 +01:00
> Committer: Borislav Petkov <[email protected]>
> CommitterDate: Tue, 29 Mar 2022 15:59:16 +02:00
>
> x86/sev: Unroll string mmio with CC_ATTR_GUEST_UNROLL_STRING_IO
>
> The io-specific memcpy/memset functions use string mmio accesses to do
> their work. Under SEV, the hypervisor can't emulate these instructions
> because they read/write directly from/to encrypted memory.
>
> KVM will inject a page fault exception into the guest when it is asked
> to emulate string mmio instructions for an SEV guest:
>
> BUG: unable to handle page fault for address: ffffc90000065068
> #PF: supervisor read access in kernel mode
> #PF: error_code(0x0000) - not-present page
> PGD 8000100000067 P4D 8000100000067 PUD 80001000fb067 PMD 80001000fc067 PTE 80000000fed40173
> Oops: 0000 [#1] PREEMPT SMP NOPTI
> CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.17.0-rc7 #3
>
> As string mmio for an SEV guest can not be supported by the
> hypervisor, unroll the instructions for CC_ATTR_GUEST_UNROLL_STRING_IO
> enabled kernels.
>
> This issue appears when kernels are launched in recent libvirt-managed
> SEV virtual machines, because virt-install started to add a tpm-crb
> device to the guest by default and proactively because, raisins:
>
> https://github.com/virt-manager/virt-manager/commit/eb58c09f488b0633ed1eea012cd311e48864401e
>
> and as that commit says, the default adding of a TPM can be disabled
> with "virt-install ... --tpm none".
>
> The kernel driver for tpm-crb uses memcpy_to/from_io() functions to
> access MMIO memory, resulting in a page-fault injected by KVM and
> crashing the kernel at boot.
>
> [ bp: Massage and extend commit message. ]
>
> Fixes: d8aa7eea78a1 ('x86/mm: Add Secure Encrypted Virtualization (SEV) support')
> Signed-off-by: Joerg Roedel <[email protected]>
> Signed-off-by: Borislav Petkov <[email protected]>
> Reviewed-by: Tom Lendacky <[email protected]>
> Cc: <[email protected]>
> Link: https://lore.kernel.org/r/[email protected]
> ---
> arch/x86/lib/iomem.c | 65 +++++++++++++++++++++++++++++++++++++------
> 1 file changed, 57 insertions(+), 8 deletions(-)
>
> diff --git a/arch/x86/lib/iomem.c b/arch/x86/lib/iomem.c
> index df50451..3e2f33f 100644
> --- a/arch/x86/lib/iomem.c
> +++ b/arch/x86/lib/iomem.c
> @@ -22,7 +22,7 @@ static __always_inline void rep_movs(void *to, const void *from, size_t n)
> : "memory");
> }
>
> -void memcpy_fromio(void *to, const volatile void __iomem *from, size_t n)
> +static void string_memcpy_fromio(void *to, const volatile void __iomem *from, size_t n)
> {
> if (unlikely(!n))
> return;
> @@ -38,9 +38,8 @@ void memcpy_fromio(void *to, const volatile void __iomem *from, size_t n)
> }
> rep_movs(to, (const void *)from, n);
> }
> -EXPORT_SYMBOL(memcpy_fromio);
>
> -void memcpy_toio(volatile void __iomem *to, const void *from, size_t n)
> +static void string_memcpy_toio(volatile void __iomem *to, const void *from, size_t n)
> {
> if (unlikely(!n))
> return;
> @@ -56,14 +55,64 @@ void memcpy_toio(volatile void __iomem *to, const void *from, size_t n)
> }
> rep_movs((void *)to, (const void *) from, n);
> }
> +
> +static void unrolled_memcpy_fromio(void *to, const volatile void __iomem *from, size_t n)
> +{
> + const volatile char __iomem *in = from;
> + char *out = to;
> + int i;
> +
> + for (i = 0; i < n; ++i)
> + out[i] = readb(&in[i]);
> +}
> +
> +static void unrolled_memcpy_toio(volatile void __iomem *to, const void *from, size_t n)
> +{
> + volatile char __iomem *out = to;
> + const char *in = from;
> + int i;
> +
> + for (i = 0; i < n; ++i)
> + writeb(in[i], &out[i]);
> +}
> +
> +static void unrolled_memset_io(volatile void __iomem *a, int b, size_t c)
> +{
> + volatile char __iomem *mem = a;
> + int i;
> +
> + for (i = 0; i < c; ++i)
> + writeb(b, &mem[i]);
> +}
> +
> +void memcpy_fromio(void *to, const volatile void __iomem *from, size_t n)
> +{
> + if (cc_platform_has(CC_ATTR_GUEST_UNROLL_STRING_IO))
> + unrolled_memcpy_fromio(to, from, n);
> + else
> + string_memcpy_fromio(to, from, n);
> +}
> +EXPORT_SYMBOL(memcpy_fromio);
> +
> +void memcpy_toio(volatile void __iomem *to, const void *from, size_t n)
> +{
> + if (cc_platform_has(CC_ATTR_GUEST_UNROLL_STRING_IO))
> + unrolled_memcpy_toio(to, from, n);
> + else
> + string_memcpy_toio(to, from, n);
> +}
> EXPORT_SYMBOL(memcpy_toio);
>
> void memset_io(volatile void __iomem *a, int b, size_t c)
> {
> - /*
> - * TODO: memset can mangle the IO patterns quite a bit.
> - * perhaps it would be better to use a dumb one:
> - */
> - memset((void *)a, b, c);
> + if (cc_platform_has(CC_ATTR_GUEST_UNROLL_STRING_IO)) {
> + unrolled_memset_io(a, b, c);
> + } else {
> + /*
> + * TODO: memset can mangle the IO patterns quite a bit.
> + * perhaps it would be better to use a dumb one:
> + */
> + memset((void *)a, b, c);
> + }
> }
> EXPORT_SYMBOL(memset_io);
-
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