* [edk2-devel] [PATCH 1/1] OvmfPkg: Align the SEC module within OvmfPkgX64
@ 2024-03-26 16:52 Glenn Griffin
2024-03-26 20:07 ` Ard Biesheuvel
0 siblings, 1 reply; 3+ messages in thread
From: Glenn Griffin @ 2024-03-26 16:52 UTC (permalink / raw)
To: devel
[-- Attachment #1: Type: text/plain, Size: 2936 bytes --]
Prior to this change the alignment of the SEC module would be 4 bytes.
This is inconsistent with the expectations of the compiler and can lead
to unexpected behavior.
For example a modern version of clang with size optimizations enabled
(-Oz) can break the ALIGN_POINTER macro in the SEC module.
Here is a minimal example:
https://godbolt.org/z/fzW67ndTY
```
unsigned char mArray[112];
#define ALIGN_VALUE(Value, Alignment) ((Value) + (((Alignment) - (Value)) & ((Alignment) - 1)))
#define ALIGN_POINTER(Pointer, Alignment) ((void *) (ALIGN_VALUE ((uint64_t)(Pointer), (Alignment))))
int main() {
printf("0x%llx\n", mArray);
printf("0x%llx\n", ALIGN_POINTER(mArray, 64));
return 0;
}
```
The above code compiles down to:
```
main: # @main
push r14
push rbx
push rax
lea rbx, [rip + .L.str]
lea r14, [rip + mArray]
mov rdi, rbx
mov rsi, r14
xor eax, eax
call printf@PLT
push 64
pop rsi
sub esi, r14d
and esi, 48
add rsi, r14
mov rdi, rbx
xor eax, eax
call printf@PLT
xor eax, eax
add rsp, 8
pop rbx
pop r14
ret
mArray:
.zero 112
.L.str:
.asciz "0x%llx\n"
```
Note that the `value & 63` in the ALIGN_VALUE implementation gets
transformed into `and esi, 48` in the assembly. The compiler knows
the array address is already aligned so it believes there is no need to
clear the last 4 bits of the address.
However by mapping the data section that contains mArray onto a
4-byte-aligned base address we violate the compiler's expectations. The
last 4 bits of the mArray address are no longer zeroes leading to an
ALIGN_POINTER macro that doesn't work.
Cc: Ard Biesheuvel <ardb+tianocore@kernel.org>
Signed-off-by: Glenn Griffin <ggriffiniii@gmail.com>
---
OvmfPkg/OvmfPkgX64.fdf | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/OvmfPkg/OvmfPkgX64.fdf b/OvmfPkg/OvmfPkgX64.fdf
index eb3fb90cb8b6..8b60355de40b 100644
--- a/OvmfPkg/OvmfPkgX64.fdf
+++ b/OvmfPkg/OvmfPkgX64.fdf
@@ -434,7 +434,7 @@ [FV.FVMAIN_COMPACT]
[Rule.Common.SEC]
FILE SEC = $(NAMED_GUID) {
- PE32 PE32 $(INF_OUTPUT)/$(MODULE_NAME).efi
+ PE32 PE32 Align=Auto $(INF_OUTPUT)/$(MODULE_NAME).efi
UI STRING ="$(MODULE_NAME)" Optional
VERSION STRING ="$(INF_VERSION)" Optional BUILD_NUM=$(BUILD_NUMBER)
}
--
2.44.0.396.g6e790dbe36-goog
-=-=-=-=-=-=-=-=-=-=-=-
Groups.io Links: You receive all messages sent to this group.
View/Reply Online (#117138): https://edk2.groups.io/g/devel/message/117138
Mute This Topic: https://groups.io/mt/105165329/7686176
Group Owner: devel+owner@edk2.groups.io
Unsubscribe: https://edk2.groups.io/g/devel/unsub [rebecca@openfw.io]
-=-=-=-=-=-=-=-=-=-=-=-
[-- Attachment #2: Type: text/html, Size: 5695 bytes --]
^ permalink raw reply related [flat|nested] 3+ messages in thread
* [edk2-devel] [PATCH 1/1] OvmfPkg: Align the SEC module within OvmfPkgX64
@ 2024-03-26 17:04 Glenn Griffin
0 siblings, 0 replies; 3+ messages in thread
From: Glenn Griffin @ 2024-03-26 17:04 UTC (permalink / raw)
To: devel
Prior to this change the alignment of the SEC module would be 4 bytes.
This is inconsistent with the expectations of the compiler and can lead
to unexpected behavior.
For example a modern version of clang with size optimizations enabled
(-Oz) can break the ALIGN_POINTER macro in the SEC module.
Here is a minimal example:
https://godbolt.org/z/fzW67ndTY
```
unsigned char mArray[112];
#define ALIGN_VALUE(Value, Alignment) ((Value) + (((Alignment) -
(Value)) & ((Alignment) - 1)))
#define ALIGN_POINTER(Pointer, Alignment) ((void *) (ALIGN_VALUE
((uint64_t)(Pointer), (Alignment))))
int main() {
printf("0x%llx\n", mArray);
printf("0x%llx\n", ALIGN_POINTER(mArray, 64));
return 0;
}
```
The above code compiles down to:
```
main: # @main
push r14
push rbx
push rax
lea rbx, [rip + .L.str]
lea r14, [rip + mArray]
mov rdi, rbx
mov rsi, r14
xor eax, eax
call printf@PLT
push 64
pop rsi
sub esi, r14d
and esi, 48
add rsi, r14
mov rdi, rbx
xor eax, eax
call printf@PLT
xor eax, eax
add rsp, 8
pop rbx
pop r14
ret
mArray:
.zero 112
.L.str:
.asciz "0x%llx\n"
```
Note that the `value & 63` in the ALIGN_VALUE implementation gets
transformed into `and esi, 48` in the assembly. The compiler knows
the array address is already aligned so it believes there is no need to
clear the last 4 bits of the address.
However by mapping the data section that contains mArray onto a
4-byte-aligned base address we violate the compiler's expectations. The
last 4 bits of the mArray address are no longer zeroes leading to an
ALIGN_POINTER macro that doesn't work.
Cc: Ard Biesheuvel <ardb+tianocore@kernel.org>
Signed-off-by: Glenn Griffin <ggriffiniii@gmail.com>
---
OvmfPkg/OvmfPkgX64.fdf | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/OvmfPkg/OvmfPkgX64.fdf b/OvmfPkg/OvmfPkgX64.fdf
index eb3fb90cb8b6..8b60355de40b 100644
--- a/OvmfPkg/OvmfPkgX64.fdf
+++ b/OvmfPkg/OvmfPkgX64.fdf
@@ -434,7 +434,7 @@ [FV.FVMAIN_COMPACT]
[Rule.Common.SEC]
FILE SEC = $(NAMED_GUID) {
- PE32 PE32 $(INF_OUTPUT)/$(MODULE_NAME).efi
+ PE32 PE32 Align=Auto $(INF_OUTPUT)/$(MODULE_NAME).efi
UI STRING ="$(MODULE_NAME)" Optional
VERSION STRING ="$(INF_VERSION)" Optional BUILD_NUM=$(BUILD_NUMBER)
}
--
2.44.0.396.g6e790dbe36-goog
-=-=-=-=-=-=-=-=-=-=-=-
Groups.io Links: You receive all messages sent to this group.
View/Reply Online (#117139): https://edk2.groups.io/g/devel/message/117139
Mute This Topic: https://groups.io/mt/105165329/7686176
Group Owner: devel+owner@edk2.groups.io
Unsubscribe: https://edk2.groups.io/g/devel/unsub [rebecca@openfw.io]
-=-=-=-=-=-=-=-=-=-=-=-
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [edk2-devel] [PATCH 1/1] OvmfPkg: Align the SEC module within OvmfPkgX64
2024-03-26 16:52 [edk2-devel] [PATCH 1/1] OvmfPkg: Align the SEC module within OvmfPkgX64 Glenn Griffin
@ 2024-03-26 20:07 ` Ard Biesheuvel
0 siblings, 0 replies; 3+ messages in thread
From: Ard Biesheuvel @ 2024-03-26 20:07 UTC (permalink / raw)
To: devel, ggriffiniii, Andrew Fish, Michael Kinney, Jiewen Yao
On Tue, 26 Mar 2024 at 22:01, Glenn Griffin <ggriffiniii@gmail.com> wrote:
>
> Prior to this change the alignment of the SEC module would be 4 bytes.
> This is inconsistent with the expectations of the compiler and can lead
> to unexpected behavior.
>
> For example a modern version of clang with size optimizations enabled
> (-Oz) can break the ALIGN_POINTER macro in the SEC module.
>
...
>
> However by mapping the data section that contains mArray onto a
> 4-byte-aligned base address we violate the compiler's expectations. The
> last 4 bits of the mArray address are no longer zeroes leading to an
> ALIGN_POINTER macro that doesn't work.
>
> Cc: Ard Biesheuvel <ardb+tianocore@kernel.org>
>
> Signed-off-by: Glenn Griffin <ggriffiniii@gmail.com>
> ---
> OvmfPkg/OvmfPkgX64.fdf | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/OvmfPkg/OvmfPkgX64.fdf b/OvmfPkg/OvmfPkgX64.fdf
> index eb3fb90cb8b6..8b60355de40b 100644
> --- a/OvmfPkg/OvmfPkgX64.fdf
> +++ b/OvmfPkg/OvmfPkgX64.fdf
> @@ -434,7 +434,7 @@ [FV.FVMAIN_COMPACT]
>
> [Rule.Common.SEC]
> FILE SEC = $(NAMED_GUID) {
> - PE32 PE32 $(INF_OUTPUT)/$(MODULE_NAME).efi
> + PE32 PE32 Align=Auto $(INF_OUTPUT)/$(MODULE_NAME).efi
> UI STRING ="$(MODULE_NAME)" Optional
> VERSION STRING ="$(INF_VERSION)" Optional BUILD_NUM=$(BUILD_NUMBER)
> }
Thanks Glenn. As you have mentioned to me off-list, this is the same
issue Andrew reported here
Link: https://bugzilla.tianocore.org/show_bug.cgi?id=3887
Your fix is obviously correct, and I intend to merge it unless anyone
has any concerns with this.
-=-=-=-=-=-=-=-=-=-=-=-
Groups.io Links: You receive all messages sent to this group.
View/Reply Online (#117140): https://edk2.groups.io/g/devel/message/117140
Mute This Topic: https://groups.io/mt/105165329/7686176
Group Owner: devel+owner@edk2.groups.io
Unsubscribe: https://edk2.groups.io/g/devel/unsub [rebecca@openfw.io]
-=-=-=-=-=-=-=-=-=-=-=-
^ permalink raw reply [flat|nested] 3+ messages in thread
end of thread, other threads:[~2024-03-26 20:07 UTC | newest]
Thread overview: 3+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2024-03-26 16:52 [edk2-devel] [PATCH 1/1] OvmfPkg: Align the SEC module within OvmfPkgX64 Glenn Griffin
2024-03-26 20:07 ` Ard Biesheuvel
-- strict thread matches above, loose matches on Subject: below --
2024-03-26 17:04 Glenn Griffin
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox