Re: [PATCH v4] PCI: Check rom header and data structure addr before accessing

[Guixin Liu]

在 2025/11/27 01:39, Andy Shevchenko 写道:
> On Wed, Nov 26, 2025 at 08:57:27PM +0800, Guixin Liu wrote:
> > We meet a crash when running stress-ng on x86_64 machine:
> >
> >    BUG: unable to handle page fault for address: ffa0000007f40000
> >    RIP: 0010:pci_get_rom_size+0x52/0x220
> >    Call Trace:
> >    <TASK>
> >      pci_map_rom+0x80/0x130
> >      pci_read_rom+0x4b/0xe0
> >      kernfs_file_read_iter+0x96/0x180
> >      vfs_read+0x1b1/0x300
> >
> > Our analysis reveals that the rom space's start address is
> > 0xffa0000007f30000, and size is 0x10000. Because of broken rom
> > space, before calling readl(pds), the pds's value is
> > 0xffa0000007f3ffff, which is already pointed to the rom space
> > end, invoking readl() would read 4 bytes therefore cause an
> > out-of-bounds access and trigger a crash.
> > Fix this by adding image header and data structure checking.
> >
> > We also found another crash on arm64 machine:
> >
> >    Unable to handle kernel paging request at virtual address
> > ffff8000dd1393ff
> >    Mem abort info:
> >    ESR = 0x0000000096000021
> >    EC = 0x25: DABT (current EL), IL = 32 bits
> >    SET = 0, FnV = 0
> >    EA = 0, S1PTW = 0
> >    FSC = 0x21: alignment fault
> >
> > The call trace is the same with x86_64, but the crash reason is
> > that the data structure addr is not aligned with 4, and arm64
> > machine report "alignment fault". Fix this by adding alignment
> > checking.
> There are few comments, but in general it looks good to me.
> So, if you address the below, feel free to add
> Reviewed-by: Andy Shevchenko <andriy.shevchenko@xxxxxxxxx>
> And thanks for pursuing this issue!
>
> ...
Added in v5, Thanks for your rb tag.
> > ---
> > v3 -> v4:
> > - Use "u64" instead of "uintptr_t".
> Hmm... Do we have a use cases when u64 is required on, say,
> 32-bit unsigned long cases?
No，I will change this to unsigned long.
> > - Invert the if statement to avoid excessive indentation.
> > - Add comment for alignment checking.
> > - Change last_image's type from int to bool.
> ...
>
> > +static inline bool pci_rom_header_valid(struct pci_dev *pdev,
> Usually we use verb 'is' in names of the boolean functions.
>
> pci_rom_is_header_valid()
Sure.
> > +					void __iomem *image,
> > +					void __iomem *rom,
> > +					size_t size,
> > +					bool last_image)
> > +{
> > +	u64 rom_end = (u64)rom + size;
> > +	u64 header_end;
> > +
> > +	/*
> > +	 * Some CPU architectures require IOMEM access addresses to
> > +	 * be aligned, for example arm64, so since we're about to
> > +	 * call readw(), we check here for 2-byte alignment.
> > +	 */
> > +	if (!IS_ALIGNED((u64)image, 2))
> > +		return false;
> > +
> > +	if (check_add_overflow((u64)image, PCI_ROM_HEADER_SIZE, &header_end))
> > +		return false;
> > +
> > +	if (image < rom || header_end >= rom_end)
> But header_end == rom_end is valid case for _header_, no? Then we should fail
> later on.
No, header_end == rom_end is invalid case, rom_end is rom+size not 
rom+size-1. Well, this is a littel bit confusing, I will change rom_end 
to rom+size-1 in v5.
> > +		return false;
> > +
> > +	/* Standard PCI ROMs start out with these bytes 55 AA */
> > +	if (readw(image) == 0xAA55)
> > +		return true;
> > +	if (!last_image)
> > +		pci_info(pdev, "No more image in the PCI ROM\n");
> > +	else
> > +		pci_info(pdev, "Invalid PCI ROM header signature: expecting 0xaa55, got %#06x\n",
> > +			 readw(image));
>
> The positive conditional can be used (easier to parse)
>
> 	if (last_image)
> 		...
> 	else
> 		...
Sure
> > +	return false;
> > +}
> > +
> > +static inline bool pci_rom_data_struct_valid(struct pci_dev *pdev,
> pci_rom_is_data_struct_valid()
Sure.
> > +					     void __iomem *pds,
> > +					     void __iomem *rom,
> > +					     size_t size)
> > +{
> > +	u64 rom_end = (u64)rom + size;
> > +	u64 end;
> > +	u16 data_len;
> > +
> > +	/*
> > +	 * Some CPU architectures require IOMEM access addresses to
> > +	 * be aligned, for example arm64, so since we're about to
> > +	 * call readl(), we check here for 4-byte alignment.
> > +	 */
> > +	if (!IS_ALIGNED((u64)pds, 4))
> > +		return false;
> > +
> > +	/* Before reading length, check range. */
> > +	if (check_add_overflow((u64)pds, 0x0B, &end))
> > +		return false;
> > +
> > +	if (pds < rom || end >= rom_end)
> Same Q here, wouldn't '=' be a valid case?
Change rom_end to rom+size-1.
> > +		return false;
> > +
> > +	data_len = readw(pds + 0x0A);
> > +	if (!data_len || data_len == 0xFFFF ||
> U16_MAX?
Sure.
> > +	    check_add_overflow((u64)pds, data_len, &end))
> > +		return false;
> I would split these two
>
> 	data_len = readw(pds + 0x0A);
> 	if (!data_len || data_len == U16_MAX)
> 		return false;
>
> 	if (check_add_overflow((u64)pds, data_len, &end))
> 		return false;
Sure.
> > +	if (end >= rom_end)
> > +		return false;
> > +
> > +	if (readl(pds) == 0x52494350)
> > +		return true;
> > +
> > +	pci_info(pdev, "Invalid PCI ROM data signature: expecting 0x52494350, got %#010x\n",
> > +		 readl(pds));
> > +	return false;
> > +}
> ...
>
> >   	image = rom;
> >   	do {
> >   		void __iomem *pds;
> > +
> > +		if (!pci_rom_header_valid(pdev, image, rom, size, true))
> >   			break;
> > +
> >   		/* get the PCI data structure and check its "PCIR" signature */
> >   		pds = image + readw(image + 24);
> > +		if (!pci_rom_data_struct_valid(pdev, pds, rom, size))
> >   			break;
> > +
> > +		last_image = !!(readb(pds + 21) & 0x80);
> !!() is not needed.
>
> 		last_image = readb(pds + 21) & 0x80;
Remove in v5, thanks.

Best Regards,
Guixin Liu
> >   		length = readw(pds + 16);
> >   		image += length * 512;
> > +
> > +		if (!pci_rom_header_valid(pdev, image, rom, size, last_image))
> >   			break;
> >   	} while (length && !last_image);