From: "H.J. Lu" <hjl.tools@gmail.com>
To: Roland McGrath <mcgrathr@google.com>
Cc: "binutils@sourceware.org" <binutils@sourceware.org>,
GDB <gdb-patches@sourceware.org>,
Bradley Nelson <bradnelson@google.com>
Subject: Re: [PATCH] Fix buffer underrun in i386-dis.c.
Date: Thu, 09 Jan 2014 18:31:00 -0000 [thread overview]
Message-ID: <CAMe9rOrf6V5g5DL7-7McsLL=L+F3AkUjZj=b-WPOGKEmf+OV0w@mail.gmail.com> (raw)
In-Reply-To: <CAB=4xhooGrDed7eSXbPOYZjx57-HOQKCQq9wwEphWAgL0=Q8Hg@mail.gmail.com>
On Thu, Jan 9, 2014 at 10:26 AM, Roland McGrath <mcgrathr@google.com> wrote:
> When disassembling any instruction without a REX prefix, the print_insn
> function touches all_prefixes[-1]. This is usually harmless in most
> builds, because the word preceding all_prefixes will probably be the
> last_seg_prefix variable and it was usually zero already. But in some
> kinds of builds, all buffer underruns are caught and cause a crash.
>
> AFAICT the obvious local workaround is in fact the proper fix. In the
> similar cases nearby, there is a PREFIX_FOO bit in the "prefixes" bitmask
> that guards use of last_foo_prefix. But there is no such bit for the REX
> prefixes. We could test "rex != 0" instead, I suppose.
>
> OK for trunk and binutils-2.24 branch and gdb-7.7 branch?
OK for trunk and binutils-2.24 branch.
Thanks.
>
> Thanks,
> Roland
>
>
> opcodes/
> 2014-01-09 Bradley Nelson <bradnelson@google.com>
> Roland McGrath <mcgrathr@google.com>
>
> * i386-dis.c (print_insn): Do not touch all_prefixes[-1] when
> last_rex_prefix is -1.
>
> --- a/opcodes/i386-dis.c
> +++ b/opcodes/i386-dis.c
> @@ -12645,7 +12645,7 @@ print_insn (bfd_vma pc, disassemble_info *info)
> }
>
> /* Check if the REX prefix is used. */
> - if (rex_ignored == 0 && (rex ^ rex_used) == 0)
> + if (rex_ignored == 0 && (rex ^ rex_used) == 0 && last_rex_prefix >= 0)
> all_prefixes[last_rex_prefix] = 0;
>
> /* Check if the SEG prefix is used. */
--
H.J.
next prev parent reply other threads:[~2014-01-09 18:31 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-01-09 18:26 Roland McGrath
2014-01-09 18:31 ` H.J. Lu [this message]
2014-01-09 19:03 ` Pedro Alves
2014-01-09 19:28 ` Roland McGrath
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