[PATCH] x86/head: Fix incorrect size value of startup_gdt_descr

[PATCH] x86/head: Fix incorrect size value of startup_gdt_descr

[Yuntao Wang]

Since the size value is added to the base address to yield the last valid
byte address of the GDT, the current size value of startup_gdt_descr is
incorrect, fix it.

Fixes: 866b556efa12 ("x86/head/64: Install startup GDT")
Signed-off-by: Yuntao Wang <ytcoode@gmail.com>
---
 arch/x86/kernel/head64.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c
index 49f7629b17f7..cfd70939a099 100644
--- a/arch/x86/kernel/head64.c
+++ b/arch/x86/kernel/head64.c
@@ -80,7 +80,7 @@ static struct desc_struct startup_gdt[GDT_ENTRIES] = {
  * while the kernel still uses a direct mapping.
  */
 static struct desc_ptr startup_gdt_descr = {
-	.size = sizeof(startup_gdt),
+	.size = sizeof(startup_gdt) - 1,
 	.address = 0,
 };
 
-- 
2.41.0

[tip: x86/boot] x86/boot: Fix incorrect startup_gdt_descr.size

[tip-bot2 for Yuntao Wang]

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

Commit-ID:     001470fed5959d01faecbd57fcf2f60294da0de1
Gitweb:        https://git.kernel.org/tip/001470fed5959d01faecbd57fcf2f60294da0de1
Author:        Yuntao Wang <ytcoode@gmail.com>
AuthorDate:    Mon, 07 Aug 2023 16:45:47 +08:00
Committer:     Ingo Molnar <mingo@kernel.org>
CommitterDate: Tue, 03 Oct 2023 10:28:29 +02:00

x86/boot: Fix incorrect startup_gdt_descr.size

Since the size value is added to the base address to yield the last valid
byte address of the GDT, the current size value of startup_gdt_descr is
incorrect (too large by one), fix it.

[ mingo: This probably never mattered, because startup_gdt[] is only used
         in a very controlled fashion - but make it consistent nevertheless. ]

Fixes: 866b556efa12 ("x86/head/64: Install startup GDT")
Signed-off-by: Yuntao Wang <ytcoode@gmail.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Link: https://lore.kernel.org/r/20230807084547.217390-1-ytcoode@gmail.com
---
 arch/x86/kernel/head64.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c
index 49f7629..bbc2179 100644
--- a/arch/x86/kernel/head64.c
+++ b/arch/x86/kernel/head64.c
@@ -80,7 +80,7 @@ static struct desc_struct startup_gdt[GDT_ENTRIES] = {
  * while the kernel still uses a direct mapping.
  */
 static struct desc_ptr startup_gdt_descr = {
-	.size = sizeof(startup_gdt),
+	.size = sizeof(startup_gdt)-1,
 	.address = 0,
 };
 

Re: [tip: x86/boot] x86/boot: Fix incorrect startup_gdt_descr.size

[H. Peter Anvin]

On October 3, 2023 1:39:57 AM PDT, tip-bot2 for Yuntao Wang <tip-bot2@linutronix.de> wrote:
>The following commit has been merged into the x86/boot branch of tip:
>
>Commit-ID:     001470fed5959d01faecbd57fcf2f60294da0de1
>Gitweb:        https://git.kernel.org/tip/001470fed5959d01faecbd57fcf2f60294da0de1
>Author:        Yuntao Wang <ytcoode@gmail.com>
>AuthorDate:    Mon, 07 Aug 2023 16:45:47 +08:00
>Committer:     Ingo Molnar <mingo@kernel.org>
>CommitterDate: Tue, 03 Oct 2023 10:28:29 +02:00
>
>x86/boot: Fix incorrect startup_gdt_descr.size
>
>Since the size value is added to the base address to yield the last valid
>byte address of the GDT, the current size value of startup_gdt_descr is
>incorrect (too large by one), fix it.
>
>[ mingo: This probably never mattered, because startup_gdt[] is only used
>         in a very controlled fashion - but make it consistent nevertheless. ]
>
>Fixes: 866b556efa12 ("x86/head/64: Install startup GDT")
>Signed-off-by: Yuntao Wang <ytcoode@gmail.com>
>Signed-off-by: Ingo Molnar <mingo@kernel.org>
>Cc: "H. Peter Anvin" <hpa@zytor.com>
>Link: https://lore.kernel.org/r/20230807084547.217390-1-ytcoode@gmail.com
>---
> arch/x86/kernel/head64.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
>diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c
>index 49f7629..bbc2179 100644
>--- a/arch/x86/kernel/head64.c
>+++ b/arch/x86/kernel/head64.c
>@@ -80,7 +80,7 @@ static struct desc_struct startup_gdt[GDT_ENTRIES] = {
>  * while the kernel still uses a direct mapping.
>  */
> static struct desc_ptr startup_gdt_descr = {
>-	.size = sizeof(startup_gdt),
>+	.size = sizeof(startup_gdt)-1,
> 	.address = 0,
> };
> 

Well, it never mattered because there wasn't enough space at the end for an extra entry, but it is still Technically Correct™.