Re: [PATCH] acpi: Fix out of bounds access in grub_acpi_xsdt_find_table()

[Mate Kukri]

We have reverted the SPCR table patches in Debian due to crashes, I
guess this might have been the reason.

On Wed, Oct 16, 2024 at 6:20 AM Benjamin Herrenschmidt
<benh@kernel.crashing.org> wrote:
>
> The calculation of the size of the table was incorrect (copy/pasta from
> grub_acpi_rsdt_find_table() I assume...). The entries are 64-bit long.
>
> This causes us to access beyond the end of the table which is causing
> crashes during boot on some systems. Typically this is causing a crash
> on VMWare when using UEFI and enabling serial autodetection, as
>
> grub_acpi_find_table (GRUB_ACPI_SPCR_SIGNATURE);
>
> Will goes past the end of the table (the SPCR table doesn't exits)
>
> Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
> ---
>  grub-core/kern/acpi.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/grub-core/kern/acpi.c b/grub-core/kern/acpi.c
> index 48ded4e2e..8ff0835d5 100644
> --- a/grub-core/kern/acpi.c
> +++ b/grub-core/kern/acpi.c
> @@ -75,7 +75,7 @@ grub_acpi_xsdt_find_table (struct
> grub_acpi_table_header *xsdt, const char *sig)
>      return 0;
>
>    ptr = (grub_unaligned_uint64_t *) (xsdt + 1);
> -  s = (xsdt->length - sizeof (*xsdt)) / sizeof (grub_uint32_t);
> +  s = (xsdt->length - sizeof (*xsdt)) / sizeof (grub_uint64_t);
>    for (; s; s--, ptr++)
>      {
>        struct grub_acpi_table_header *tbl;
>