lkml.org 
[lkml]   [2018]   [Oct]   [5]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH] bpf: 32-bit RSH verification must truncate input before the ALU op
From
Date
On 10/05/2018 06:17 PM, Jann Horn wrote:
> When I wrote commit 468f6eafa6c4 ("bpf: fix 32-bit ALU op verification"), I
> assumed that, in order to emulate 64-bit arithmetic with 32-bit logic, it
> is sufficient to just truncate the output to 32 bits; and so I just moved
> the register size coercion that used to be at the start of the function to
> the end of the function.
>
> That assumption is true for almost every op, but not for 32-bit right
> shifts, because those can propagate information towards the least
> significant bit. Fix it by always truncating inputs for 32-bit ops to 32
> bits.
>
> Also get rid of the coerce_reg_to_size() after the ALU op, since that has
> no effect.
>
> Fixes: 468f6eafa6c4 ("bpf: fix 32-bit ALU op verification")
> Acked-by: Daniel Borkmann <daniel@iogearbox.net>
> Signed-off-by: Jann Horn <jannh@google.com>

Applied to bpf, thanks Jann!

\
 
 \ /
  Last update: 2018-10-05 19:48    [W:0.030 / U:0.188 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site