linux-kernel - Re: [PATCH] riscv: elf: add .riscv.attributes parsing

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Message-ID: <6dcdd143-ff1c-41f7-9f46-0c4505575669@rivosinc.com>
Date:   Tue, 10 Jan 2023 13:50:56 -0800
From:   Vineet Gupta <vineetg@...osinc.com>
To:     Jessica Clarke <jrtc27@...c27.com>
Cc:     linux-riscv <linux-riscv@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        palmer@...osinc.com, Paul Walmsley <paul.walmsley@...ive.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Eric Biederman <ebiederm@...ssion.com>,
        Kees Cook <keescook@...omium.org>, Guo Ren <guoren@...nel.org>,
        Greentime Hu <greentime.hu@...ive.com>,
        Conor Dooley <conor.dooley@...rochip.com>, linux@...osinc.com,
        kernel test robot <lkp@...el.com>
Subject: Re: [PATCH] riscv: elf: add .riscv.attributes parsing



On 1/10/23 12:48, Jessica Clarke wrote:
> On 10 Jan 2023, at 20:18, Vineet Gupta <vineetg@...osinc.com> 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@...el.com>  # code under CONFIG_COMPAT
>> Signed-off-by: Vineet Gupta <vineetg@...osinc.com>
> 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.


> 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

> 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