Re: [edk2-devel] [PATCH 1/1] OvmfPkg/VirtNorFlashDxe: fix shadowbuffer reads

["Laszlo Ersek" <lersek@redhat.com>]

On 1/11/24 14:36, Gerd Hoffmann wrote:
> In some cases (specifically when the flash update region is
> small but crosses a multiple of P30_MAX_BUFFER_SIZE_IN_BYTES)
> NorFlashWriteSingleBlock reads only one instead of two
> P30_MAX_BUFFER_SIZE_IN_BYTES blocks into the shadow buffer.
> 
> That leads to random crap being written to the second block,
> which in turn can corrupt both the variable store and the
> FTW work space.
> 
> This patch fixes the calculation.
> 
> Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
> ---
>  OvmfPkg/VirtNorFlashDxe/VirtNorFlash.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/OvmfPkg/VirtNorFlashDxe/VirtNorFlash.c b/OvmfPkg/VirtNorFlashDxe/VirtNorFlash.c
> index 1afd60ce66eb..cdc809d75e3d 100644
> --- a/OvmfPkg/VirtNorFlashDxe/VirtNorFlash.c
> +++ b/OvmfPkg/VirtNorFlashDxe/VirtNorFlash.c
> @@ -566,7 +566,7 @@ NorFlashWriteSingleBlock (
>                 Instance,
>                 Lba,
>                 Offset & ~BOUNDARY_OF_32_WORDS,
> -               (*NumBytes | BOUNDARY_OF_32_WORDS) + 1,
> +               (((Offset & BOUNDARY_OF_32_WORDS) + *NumBytes) | BOUNDARY_OF_32_WORDS) + 1,
>                 Instance->ShadowBuffer
>                 );
>      if (EFI_ERROR (Status)) {

This patch looks like the output of an excellent bug analysis. I'll need
more time to review this. If you have a ticket with the analysis
captured (actual numbers, debugging logs, a concrete backtrace / call
chain triggering the issue, etc), I'd appreciate a reference. (Perhaps
include some of the key items in the commit message too?)

Thanks
Laszlo



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