linux-kernel - Re: [PATCH] PCI/AER: Avoid info leak in __print_tlp

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Date:	Wed, 25 Feb 2015 19:54:23 +0100
From:	Borislav Petkov <bp@...e.de>
To:	Rasmus Villemoes <linux@...musvillemoes.dk>
Cc:	Bjorn Helgaas <bhelgaas@...gle.com>, linux-pci@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] PCI/AER: Avoid info leak in __print_tlp_header

On Tue, Feb 24, 2015 at 11:50:46PM +0100, Rasmus Villemoes wrote:
> Commit fab4c256a58b ("PCI/AER: Add a TLP header print helper")
> introduced the helper function __print_tlp_header, but contrary to the
> intention, the behaviour did change: Since we're taking the address of

Whoops, good catch.

> the parameter t, the first 4 or 8 bytes printed will be the value of
> the pointer t itself, and the remaining 12 or 8 bytes will be
> who-knows-what (something from the stack).
> 
> We want to treat the four members of the struct aer_header_log_regs as
> little-endian 32 bit numbers and print those. That can be done without
> ugly and confusing casts.
> 
> Fixes: fab4c256a58b ("PCI/AER: Add a TLP header print helper")
> Signed-off-by: Rasmus Villemoes <linux@...musvillemoes.dk>
> ---
>  drivers/pci/pcie/aer/aerdrv_errprint.c | 13 +++----------
>  1 file changed, 3 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/pci/pcie/aer/aerdrv_errprint.c b/drivers/pci/pcie/aer/aerdrv_errprint.c
> index c6849d9e86ce..e328978038c1 100644
> --- a/drivers/pci/pcie/aer/aerdrv_errprint.c
> +++ b/drivers/pci/pcie/aer/aerdrv_errprint.c
> @@ -132,16 +132,9 @@ static const char *aer_agent_string[] = {
>  static void __print_tlp_header(struct pci_dev *dev,
>  			       struct aer_header_log_regs *t)
>  {
> -	unsigned char *tlp = (unsigned char *)&t;
> -
> -	dev_err(&dev->dev, "  TLP Header:"
> -		" %02x%02x%02x%02x %02x%02x%02x%02x"
> -		" %02x%02x%02x%02x %02x%02x%02x%02x\n",
> -		*(tlp + 3), *(tlp + 2), *(tlp + 1), *tlp,
> -		*(tlp + 7), *(tlp + 6), *(tlp + 5), *(tlp + 4),
> -		*(tlp + 11), *(tlp + 10), *(tlp + 9),
> -		*(tlp + 8), *(tlp + 15), *(tlp + 14),
> -		*(tlp + 13), *(tlp + 12));
> +	dev_err(&dev->dev, "  TLP Header: %08x %08x %08x %08x\n",
> +		le32_to_cpu(t->dw0), le32_to_cpu(t->dw1),
> +		le32_to_cpu(t->dw2), le32_to_cpu(t->dw3));

I'm not sure about this: I think the original intention was to dump the
dwords MS-bit to LS-bit like this here:

http://www.fpga4fun.com/PCI-Express4.html

Now, if this runs on a big endian machine, converting to CPU order would
be wrong IMHO. You'd rather want do do cpu_to_le32() for consistency.
But I don't know whether big endian machines are even sporting PCIE
AER...

Bjorn?

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
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