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Re: [PATCH v6 3/3] x86/boot: Improve MBI2 structure check
- To: Frediano Ziglio <frediano.ziglio@xxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Mon, 30 Sep 2024 17:55:28 +0200
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- Cc: "Daniel P. Smith" <dpsmith@xxxxxxxxxxxxxxxxxxxx>, Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- Delivery-date: Mon, 30 Sep 2024 15:55:37 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 26.09.2024 11:21, Frediano Ziglio wrote:
> --- a/xen/arch/x86/efi/parse-mbi2.c
> +++ b/xen/arch/x86/efi/parse-mbi2.c
> @@ -13,6 +13,7 @@ efi_multiboot2_prelude(uint32_t magic, const
> multiboot2_fixed_t *mbi)
> EFI_HANDLE ImageHandle = NULL;
> EFI_SYSTEM_TABLE *SystemTable = NULL;
> const char *cmdline = NULL;
> + const void *const mbi_end = (const void *)mbi + mbi->total_size;
> bool have_bs = false;
>
> if ( magic != MULTIBOOT2_BOOTLOADER_MAGIC )
> @@ -21,7 +22,9 @@ efi_multiboot2_prelude(uint32_t magic, const
> multiboot2_fixed_t *mbi)
> /* Skip Multiboot2 information fixed part. */
> tag = _p(ROUNDUP((unsigned long)(mbi + 1), MULTIBOOT2_TAG_ALIGN));
>
> - for ( ; (const void *)tag - (const void *)mbi < mbi->total_size &&
> + for ( ; (const void *)(tag + 1) <= mbi_end &&
It may be possible to argue away overflow concerns here. I'm not so sure though
for the case ...
> + tag->size >= sizeof(*tag) &&
> + (const void *)tag + tag->size <= mbi_end &&
... here. The earlier logic subtracting pointers wasn't susceptible to such.
Jan
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