linux-kernel - [PATCH v4 03/15] x86/sev: Make the VMPL0 checking more straight forward

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Date: Wed, 24 Apr 2024 10:57:59 -0500
From: Tom Lendacky <thomas.lendacky@....com>
To: <linux-kernel@...r.kernel.org>, <x86@...nel.org>,
	<linux-coco@...ts.linux.dev>, <svsm-devel@...onut-svsm.dev>
CC: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
	Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>,
	"H. Peter Anvin" <hpa@...or.com>, Andy Lutomirski <luto@...nel.org>, "Peter
 Zijlstra" <peterz@...radead.org>, Dan Williams <dan.j.williams@...el.com>,
	Michael Roth <michael.roth@....com>, Ashish Kalra <ashish.kalra@....com>
Subject: [PATCH v4 03/15] 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@....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 5ad0ff4664f1..0457a9d7e515 100644
--- a/arch/x86/boot/compressed/sev.c
+++ b/arch/x86/boot/compressed/sev.c
@@ -335,26 +335,6 @@ void do_boot_stage2_vc(struct pt_regs *regs, unsigned long exit_code)
 		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))
-- 
2.43.2