* [PATCH] Fix buffer underrun in i386-dis.c.
@ 2014-01-09 18:26 Roland McGrath
2014-01-09 18:31 ` H.J. Lu
0 siblings, 1 reply; 4+ messages in thread
From: Roland McGrath @ 2014-01-09 18:26 UTC (permalink / raw)
To: binutils, gdb-patches; +Cc: Bradley Nelson
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?
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. */
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] Fix buffer underrun in i386-dis.c.
2014-01-09 18:26 [PATCH] Fix buffer underrun in i386-dis.c Roland McGrath
@ 2014-01-09 18:31 ` H.J. Lu
2014-01-09 19:03 ` Pedro Alves
0 siblings, 1 reply; 4+ messages in thread
From: H.J. Lu @ 2014-01-09 18:31 UTC (permalink / raw)
To: Roland McGrath; +Cc: binutils, GDB, Bradley Nelson
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.
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] Fix buffer underrun in i386-dis.c.
2014-01-09 18:31 ` H.J. Lu
@ 2014-01-09 19:03 ` Pedro Alves
2014-01-09 19:28 ` Roland McGrath
0 siblings, 1 reply; 4+ messages in thread
From: Pedro Alves @ 2014-01-09 19:03 UTC (permalink / raw)
To: Roland McGrath; +Cc: H.J. Lu, binutils, GDB, Bradley Nelson
On 01/09/2014 06:31 PM, H.J. Lu wrote:
> 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.
In that case, OK for gdb-7.7 too.
--
Pedro Alves
^ permalink raw reply [flat|nested] 4+ messages in thread
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2014-01-09 18:26 [PATCH] Fix buffer underrun in i386-dis.c Roland McGrath
2014-01-09 18:31 ` H.J. Lu
2014-01-09 19:03 ` Pedro Alves
2014-01-09 19:28 ` Roland McGrath
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