Re: [PATCH] riscv: elf: add .riscv.attributes parsing

[Jessica Clarke]

On 10 Jan 2023, at 21:50, Vineet Gupta <vineetg@xxxxxxxxxxxx> wrote:
> On 1/10/23 12:48, Jessica Clarke wrote:
>> On 10 Jan 2023, at 20:18, Vineet Gupta <vineetg@xxxxxxxxxxxx> wrote:
>>> This implements the elf loader hook to parse RV specific
>>> .riscv.attributes section. This section is inserted by compilers
>>> (gcc/llvm) with build related information such as -march organized as
>>> tag/value attribute pairs.
>>> 
>>> It identifies the various attribute tags (and corresponding values) as
>>> currently specified in the psABI specification.
>>> 
>>> This patch only implements the elf parsing mechanics, leaving out the
>>> recording/usage of the attributes to subsequent patches.
>>> 
>>> Reported-by: kernel test robot <lkp@xxxxxxxxx>  # code under CONFIG_COMPAT
>>> Signed-off-by: Vineet Gupta <vineetg@xxxxxxxxxxxx>
>> This code is full of buffer overruns and uninitialised reads in the
>> presence of malicious files,
> 
> While the outer loop is bound, indeed the internal pointer increments could get oob.
> I don't recall seeing existing explicit "safe" pointer, so thinking of cooking something up.
> The conceptual idea is to replace
> 
>     p += 4
> 
> with
> 
>    PTR_INC(p, 4, p_max)
> 
> And similarly replace
> 
>     while (*p++ != '\0')
> 
> with
> 
>     while (*p != '\0')
>           PTR_INC(p, 1, p_max)
> 
> Is that sufficient or you had something else in mind.

I’d be very careful about obfuscating control flow but how you
implement it is between you and other kernel developers, which I don’t
count myself as.

>> and fails to check the version, vendor and sub-subsection tag.
> 
> That is now added.
> 
>> You also should handle more than one sub-subsection even if tools don’t
>> emit it today.
> 
> Just to be on same page, a sub-section implies the following
> 
>       uint32:len, NTBS:vendor-name, uint8: Tag_file, uint32:data-len, <tag><value>....
> 
> If so, the code does support multiple of these

That’s a sub-section, but I said sub-subsection.

Jess

>> You also have an unaligned access for reading the sub-subsection’s data
>> length (maybe that’s ok in kernel land, but worth making sure).
> 
> True, I've added get_unaligned_le32 for those now
> 
> Thx,
> -Vineet