[v1] x86/sev: Fix operator precedence in GHCB_MSR_VMPL_REQ_LEVEL macro

[PATCH] x86/sev: Fix operator precedence in GHCB_MSR_VMPL_REQ_LEVEL macro

Posted by Seongmanlee 7 months, 1 week ago

From: leonardo-leecaprio <augustus92@kaist.ac.kr>

The GHCB_MSR_VMPL_REQ_LEVEL macro lacked parentheses around the bitmask
expression, causing the shift operation to bind too early. As a result,
when switching to VMPL2 from VMPL1 (e.g., GHCB_MSR_VMPL_REQ_LEVEL(1)),
incorrect values such as 0x000000016 were generated instead of the intended
0x100000016.

This patch fixes the precedence issue by grouping the masked value
before applying the shift.

Signed-off-by: leonardo-leecaprio <augustus92@kaist.ac.kr>
---
 arch/x86/include/asm/sev-common.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/sev-common.h b/arch/x86/include/asm/sev-common.h
index acb85b934..0020d77a0 100644
--- a/arch/x86/include/asm/sev-common.h
+++ b/arch/x86/include/asm/sev-common.h
@@ -116,7 +116,7 @@ enum psc_op {
 #define GHCB_MSR_VMPL_REQ		0x016
 #define GHCB_MSR_VMPL_REQ_LEVEL(v)			\
 	/* GHCBData[39:32] */				\
-	(((u64)(v) & GENMASK_ULL(7, 0) << 32) |		\
+	((((u64)(v) & GENMASK_ULL(7, 0)) << 32) |	\
 	/* GHCBDdata[11:0] */				\
 	GHCB_MSR_VMPL_REQ)
 
-- 
2.39.5 (Apple Git-154)

Re: [PATCH] x86/sev: Fix operator precedence in GHCB_MSR_VMPL_REQ_LEVEL macro

Posted by Borislav Petkov 7 months ago

+ Tom.

On Sun, May 11, 2025 at 01:27:24AM +0900, Seongmanlee wrote:
> From: leonardo-leecaprio <augustus92@kaist.ac.kr>
> 
> The GHCB_MSR_VMPL_REQ_LEVEL macro lacked parentheses around the bitmask
> expression, causing the shift operation to bind too early. As a result,
> when switching to VMPL2 from VMPL1 (e.g., GHCB_MSR_VMPL_REQ_LEVEL(1)),
> incorrect values such as 0x000000016 were generated instead of the intended
> 0x100000016.
> 
> This patch fixes the precedence issue by grouping the masked value

Avoid having "This patch" or "This commit" in the commit message. It is
tautologically useless.

Also, do

$ git grep 'This patch' Documentation/process

for more details.

> before applying the shift.
> 

Fixes: 34ff65901735 ("x86/sev: Use kernel provided SVSM Calling Areas")

> Signed-off-by: leonardo-leecaprio <augustus92@kaist.ac.kr>

Please use your real name.

> ---
>  arch/x86/include/asm/sev-common.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/include/asm/sev-common.h b/arch/x86/include/asm/sev-common.h
> index acb85b934..0020d77a0 100644
> --- a/arch/x86/include/asm/sev-common.h
> +++ b/arch/x86/include/asm/sev-common.h
> @@ -116,7 +116,7 @@ enum psc_op {
>  #define GHCB_MSR_VMPL_REQ		0x016
>  #define GHCB_MSR_VMPL_REQ_LEVEL(v)			\
>  	/* GHCBData[39:32] */				\
> -	(((u64)(v) & GENMASK_ULL(7, 0) << 32) |		\
> +	((((u64)(v) & GENMASK_ULL(7, 0)) << 32) |	\
>  	/* GHCBDdata[11:0] */				\
>  	GHCB_MSR_VMPL_REQ)
>  

Thx.

-- 
Regards/Gruss,
    Boris.

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