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

[tip-bot2 for Tom Lendacky]

The following commit has been merged into the x86/urgent branch of tip:

Commit-ID:     cdaa0a407f1acd3a44861e3aea6e3c7349e668f1
Gitweb:        https://git.kernel.org/tip/cdaa0a407f1acd3a44861e3aea6e3c7349e668f1
Author:        Tom Lendacky <thomas.lendacky@xxxxxxx>
AuthorDate:    Tue, 23 Aug 2022 16:55:51 -05:00
Committer:     Borislav Petkov <bp@xxxxxxx>
CommitterDate: Wed, 24 Aug 2022 09:54:32 +02:00

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@xxxxxxxxxx>
Suggested-by: Sean Christopherson <seanjc@xxxxxxxxxx>
Signed-off-by: Tom Lendacky <thomas.lendacky@xxxxxxx>
Signed-off-by: Borislav Petkov <bp@xxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx> # 5.19.x
Link: https://lore.kernel.org/all/YqfabnTRxFSM+LoX@xxxxxxxxxx/
---
 arch/x86/kernel/sev.c | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c
index 63dc626..4f84c3f 100644
--- 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. */