linux-kernel - [PATCH] x86/sev-es: Remove subtraction of res variable

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Date:   Tue, 23 Feb 2021 12:11:30 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Joerg Roedel <joro@...tes.org>
Cc:     X86 ML <x86@...nel.org>, LKML <linux-kernel@...r.kernel.org>
Subject: [PATCH] x86/sev-es: Remove subtraction of res variable

From: Borislav Petkov <bp@...e.de>

vc_decode_insn() calls copy_from_kernel_nofault() by way of
vc_fetch_insn_kernel() to fetch 15 bytes max of opcodes to decode.

copy_from_kernel_nofault() returns negative on error and 0 on success.
The error case is handled by returning ES_EXCEPTION.

In the success case, the ret variable which contains the return value is
0 so there's no need to subtract it from MAX_INSN_SIZE when initializing
the insn buffer for further decoding. Remove it.

No functional changes.

Signed-off-by: Borislav Petkov <bp@...e.de>
---
 arch/x86/kernel/sev-es.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kernel/sev-es.c b/arch/x86/kernel/sev-es.c
index 84c1821819af..1e78f4bd7bf2 100644
--- a/arch/x86/kernel/sev-es.c
+++ b/arch/x86/kernel/sev-es.c
@@ -267,7 +267,7 @@ static enum es_result vc_decode_insn(struct es_em_ctxt *ctxt)
 			return ES_EXCEPTION;
 		}

-		insn_init(&ctxt->insn, buffer, MAX_INSN_SIZE - res, 1);
+		insn_init(&ctxt->insn, buffer, MAX_INSN_SIZE, 1);
 		insn_get_length(&ctxt->insn);
 	}

-- 
2.29.2