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Smith" , =?utf-8?q?Marek_Marczykow?= =?utf-8?q?ski-G=C3=B3recki?= , Jan Beulich , Andrew Cooper , =?utf-8?q?Roger_Pau_Monn=C3=A9?= Subject: [PATCH v8 2/2] x86/boot: Improve MBI2 structure check Date: Wed, 9 Oct 2024 09:04:39 +0100 Message-Id: <20241009080439.2411730-3-frediano.ziglio@cloud.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20241009080439.2411730-1-frediano.ziglio@cloud.com> References: <20241009080439.2411730-1-frediano.ziglio@cloud.com> MIME-Version: 1.0 Tag structure should contain at least the tag header. Entire tag structure must be contained inside MBI2 data. Signed-off-by: Frediano Ziglio Reviewed-by: Jan Beulich --- Changes since v6: - compare against total_size every time to avoid overflows. Changes since v7: - check for tag type being MULTIBOOT2_TAG_TYPE_END before checking tag size. This allows caller to not fill full tag (type field is before size field). --- xen/arch/x86/efi/mbi2.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) diff --git a/xen/arch/x86/efi/mbi2.c b/xen/arch/x86/efi/mbi2.c index 55a1777483..d2f0f0ee61 100644 --- a/xen/arch/x86/efi/mbi2.c +++ b/xen/arch/x86/efi/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_raw = (const void *)mbi; bool have_bs = false; if ( magic != MULTIBOOT2_BOOTLOADER_MAGIC ) @@ -21,8 +22,10 @@ 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 && - tag->type != MULTIBOOT2_TAG_TYPE_END; + for ( ; (const void *)(tag + 1) - mbi_raw <= mbi->total_size && + tag->type != MULTIBOOT2_TAG_TYPE_END && + tag->size >= sizeof(*tag) && + (const void *)tag + tag->size - mbi_raw <= mbi->total_size; tag = _p(ROUNDUP((unsigned long)tag + tag->size, MULTIBOOT2_TAG_ALIGN)) ) {