x86/sev: Don't use cc_platform_has() for early SEV-SNP calls

When running identity-mapped and depending on the kernel configuration,
it is possible that the compiler uses jump tables when generating code
for cc_platform_has().

This causes a boot failure because the jump table uses un-mapped kernel
virtual addresses, not identity-mapped addresses. This has been seen
with CONFIG_RETPOLINE=n.

Similar to sme_encrypt_kernel(), use an open-coded direct check for the
status of SNP rather than trying to eliminate the jump table. This
preserves any code optimization in cc_platform_has() that can be useful
post boot. It also limits the changes to SEV-specific files so that
future compiler features won't necessarily require possible build changes
just because they are not compatible with running identity-mapped.

  [ bp: Massage commit message. ]

Fixes: 5e5ccff60a29 ("x86/sev: Add helper for validating pages in early enc attribute changes")
Reported-by: Sean Christopherson <seanjc@google.com>
Suggested-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Cc: <stable@vger.kernel.org> # 5.19.x
Link: https://lore.kernel.org/all/YqfabnTRxFSM+LoX@google.com/

diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c
index 63dc626627a03ed1a4d0df7b5fb19fa9021b10b0..4f84c3f11af5b60cfe1a9d6d68b1823d4b74c532 100644 (file)
--- a/arch/x86/kernel/sev.c
+++ b/arch/x86/kernel/sev.c
@@ -701,7 +701,13 @@ e_term:
 void __init early_snp_set_memory_private(unsigned long vaddr, unsigned long paddr,
                                         unsigned int npages)
 {
-       if (!cc_platform_has(CC_ATTR_GUEST_SEV_SNP))
+       /*
+        * This can be invoked in early boot while running identity mapped, so
+        * use an open coded check for SNP instead of using cc_platform_has().
+        * This eliminates worries about jump tables or checking boot_cpu_data
+        * in the cc_platform_has() function.
+        */
+       if (!(sev_status & MSR_AMD64_SEV_SNP_ENABLED))
                return;
 
         /*
@@ -717,7 +723,13 @@ void __init early_snp_set_memory_private(unsigned long vaddr, unsigned long padd
 void __init early_snp_set_memory_shared(unsigned long vaddr, unsigned long paddr,
                                        unsigned int npages)
 {
-       if (!cc_platform_has(CC_ATTR_GUEST_SEV_SNP))
+       /*
+        * This can be invoked in early boot while running identity mapped, so
+        * use an open coded check for SNP instead of using cc_platform_has().
+        * This eliminates worries about jump tables or checking boot_cpu_data
+        * in the cc_platform_has() function.
+        */
+       if (!(sev_status & MSR_AMD64_SEV_SNP_ENABLED))
                return;
 
        /* Invalidate the memory pages before they are marked shared in the RMP table. */