6.16-stable review patch. If anyone has any objections, please let me know.
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From: Gerd Hoffmann kraxel@redhat.com
[ Upstream commit 7b22e0432981c2fa230f1b493082b7e67112c4aa ]
In case efi_mm is active go use the userspace instruction decoder which supports fetching instructions from active_mm. This is needed to make instruction emulation work for EFI runtime code, so it can use CPUID and RDMSR.
EFI runtime code uses the CPUID instruction to gather information about the environment it is running in, such as SEV being enabled or not, and choose (if needed) the SEV code path for ioport access.
EFI runtime code uses the RDMSR instruction to get the location of the CAA page (see SVSM spec, section 4.2 - "Post Boot").
The big picture behind this is that the kernel needs to be able to properly handle #VC exceptions that come from EFI runtime services. Since EFI runtime services have a special page table mapping for the EFI virtual address space, the efi_mm context must be used when decoding instructions during #VC handling.
[ bp: Massage. ]
Signed-off-by: Gerd Hoffmann kraxel@redhat.com Signed-off-by: Borislav Petkov (AMD) bp@alien8.de Reviewed-by: Pankaj Gupta pankaj.gupta@amd.com Link: https://lore.kernel.org/20250626114014.373748-2-kraxel@redhat.com Signed-off-by: Sasha Levin sashal@kernel.org --- arch/x86/coco/sev/vc-handle.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-)
diff --git a/arch/x86/coco/sev/vc-handle.c b/arch/x86/coco/sev/vc-handle.c index 0989d98da130..faf1fce89ed4 100644 --- a/arch/x86/coco/sev/vc-handle.c +++ b/arch/x86/coco/sev/vc-handle.c @@ -17,6 +17,7 @@ #include <linux/mm.h> #include <linux/io.h> #include <linux/psp-sev.h> +#include <linux/efi.h> #include <uapi/linux/sev-guest.h>
#include <asm/init.h> @@ -178,9 +179,15 @@ static enum es_result __vc_decode_kern_insn(struct es_em_ctxt *ctxt) return ES_OK; }
+/* + * User instruction decoding is also required for the EFI runtime. Even though + * the EFI runtime is running in kernel mode, it uses special EFI virtual + * address mappings that require the use of efi_mm to properly address and + * decode. + */ static enum es_result vc_decode_insn(struct es_em_ctxt *ctxt) { - if (user_mode(ctxt->regs)) + if (user_mode(ctxt->regs) || mm_is_efi(current->active_mm)) return __vc_decode_user_insn(ctxt); else return __vc_decode_kern_insn(ctxt);