Mailing List Archive

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

Commit-ID: e2f4c8c319abd1afbedb7a31877cb569265db1b4
Gitweb: https://git.kernel.org/tip/e2f4c8c319abd1afbedb7a31877cb569265db1b4
Author: Tom Lendacky <thomas.lendacky@amd.com>
AuthorDate: Wed, 24 Apr 2024 10:57:59 -05:00
Committer: Borislav Petkov (AMD) <bp@alien8.de>
CommitterDate: Thu, 25 Apr 2024 16:14:25 +02:00

x86/sev: Make the VMPL0 checking more straight forward

Currently, the enforce_vmpl0() function uses a set argument when modifying
the VMPL1 permissions used to test for VMPL0. If the guest is not running
at VMPL0, the guest self-terminates.

The function is just a wrapper for a fixed RMPADJUST function. Eliminate
the function and perform the RMPADJUST directly.

No functional change.

Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/ed01ddf04bfb475596b24b634fd26cffaa85173a.1713974291.git.thomas.lendacky@amd.com
---
arch/x86/boot/compressed/sev.c | 35 +++++++++++++--------------------
1 file changed, 14 insertions(+), 21 deletions(-)

diff --git a/arch/x86/boot/compressed/sev.c b/arch/x86/boot/compressed/sev.c
index 5ad0ff4..0457a9d 100644
--- a/arch/x86/boot/compressed/sev.c
+++ b/arch/x86/boot/compressed/sev.c
@@ -335,26 +335,6 @@ finish:
sev_es_terminate(SEV_TERM_SET_GEN, GHCB_SEV_ES_GEN_REQ);
}

-static void enforce_vmpl0(void)
-{
- u64 attrs;
- int err;
-
- /*
- * RMPADJUST modifies RMP permissions of a lesser-privileged (numerically
- * higher) privilege level. Here, clear the VMPL1 permission mask of the
- * GHCB page. If the guest is not running at VMPL0, this will fail.
- *
- * If the guest is running at VMPL0, it will succeed. Even if that operation
- * modifies permission bits, it is still ok to do so currently because Linux
- * SNP guests are supported only on VMPL0 so VMPL1 or higher permission masks
- * changing is a don't-care.
- */
- attrs = 1;
- if (rmpadjust((unsigned long)&boot_ghcb_page, RMP_PG_SIZE_4K, attrs))
- sev_es_terminate(SEV_TERM_SET_LINUX, GHCB_TERM_NOT_VMPL0);
-}
-
/*
* SNP_FEATURES_IMPL_REQ is the mask of SNP features that will need
* guest side implementation for proper functioning of the guest. If any
@@ -588,7 +568,20 @@ void sev_enable(struct boot_params *bp)
if (!(get_hv_features() & GHCB_HV_FT_SNP))
sev_es_terminate(SEV_TERM_SET_GEN, GHCB_SNP_UNSUPPORTED);

- enforce_vmpl0();
+ /*
+ * Enforce running at VMPL0.
+ *
+ * RMPADJUST modifies RMP permissions of a lesser-privileged (numerically
+ * higher) privilege level. Here, clear the VMPL1 permission mask of the
+ * GHCB page. If the guest is not running at VMPL0, this will fail.
+ *
+ * If the guest is running at VMPL0, it will succeed. Even if that operation
+ * modifies permission bits, it is still ok to do so currently because Linux
+ * SNP guests running at VMPL0 only run at VMPL0, so VMPL1 or higher
+ * permission mask changes are a don't-care.
+ */
+ if (rmpadjust((unsigned long)&boot_ghcb_page, RMP_PG_SIZE_4K, 1))
+ sev_es_terminate(SEV_TERM_SET_LINUX, GHCB_TERM_NOT_VMPL0);
}

if (snp && !(sev_status & MSR_AMD64_SEV_SNP_ENABLED))