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authorJoerg Roedel <jroedel@suse.de>2022-03-21 10:33:51 +0100
committerBorislav Petkov <bp@suse.de>2022-03-29 15:59:16 +0200
commit4009a4ac82dd95b8cd2b62bd30019476983f0aff (patch)
tree0bbd66c668d689fd7ddb4521defc25945f56b674
parentx86/config: Make the x86 defconfigs a bit more usable (diff)
downloadlinux-4009a4ac82dd95b8cd2b62bd30019476983f0aff.tar.xz
linux-4009a4ac82dd95b8cd2b62bd30019476983f0aff.zip
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 <jroedel@suse.de> Signed-off-by: Borislav Petkov <bp@suse.de> Reviewed-by: Tom Lendacky <thomas.lendacky@amd.com> Cc: <stable@vger.kernel.org> Link: https://lore.kernel.org/r/20220321093351.23976-1-joro@8bytes.org
-rw-r--r--arch/x86/lib/iomem.c65
1 files changed, 57 insertions, 8 deletions
diff --git a/arch/x86/lib/iomem.c b/arch/x86/lib/iomem.c
index df50451d94ef..3e2f33fc33de 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);