Re: [PATCH v1 1/4] perf tools: Prevent out-of-bounds access to registers

[Arnaldo Carvalho de Melo]

On December 10, 2021 12:28:56 PM GMT-03:00, German Gomez <german.gomez at arm.com> wrote:
>
>On 10/12/2021 13:38, Arnaldo Carvalho de Melo wrote:
>> Em Fri, Dec 10, 2021 at 02:47:49PM +0530, kajoljain escreveu:
>>>
>>> On 12/1/21 6:03 PM, German Gomez wrote:
>>>> The size of the cache of register values is arch-dependant
>>>> (PERF_REGS_MAX). This has the potential of causing an out-of-bounds
>>>> access in the function "perf_reg_value" if the local architecture
>>>> contains less registers than the one the perf.data file was recorded on.
>>>>
>>>> Since the maximum number of registers is bound by the bitmask "u64
>>>> cache_mask", and the size of the cache when running under x86 systems is
>>>> 64 already, fix the size to 64 and add a range-check to the function
>>>> "perf_reg_value" to prevent out-of-bounds access.
>>>>
>>> Patch looks good to me.
>>>
>>> Reviewed-by: Kajol Jain<kjain at linux.ibm.com>
>> Thanks, applied.
>>
>> - Arnaldo
>
>Thanks Arnaldo, and the rest for the review.
>
>I did send a v2 of this patch afterwards. The only difference was to
>give credit to the reporter in the commit message with:
>
>Reported-by: Alexandre Truong <alexandre.truong at arm.com>


I'll add it.

- Arnaldo
>
>Thanks,
>German
>
>>  
>>> Thanks,
>>> Kajol Jain
>>>
>>>> Signed-off-by: German Gomez <german.gomez at arm.com>
>>>> ---
>>>>  tools/perf/util/event.h     | 5 ++++-
>>>>  tools/perf/util/perf_regs.c | 3 +++
>>>>  2 files changed, 7 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/tools/perf/util/event.h b/tools/perf/util/event.h
>>>> index 95ffed663..c59331eea 100644
>>>> --- a/tools/perf/util/event.h
>>>> +++ b/tools/perf/util/event.h
>>>> @@ -44,13 +44,16 @@ struct perf_event_attr;
>>>>  /* perf sample has 16 bits size limit */
>>>>  #define PERF_SAMPLE_MAX_SIZE (1 << 16)
>>>>  
>>>> +/* number of register is bound by the number of bits in regs_dump::mask (64) */
>>>> +#define PERF_SAMPLE_REGS_CACHE_SIZE (8 * sizeof(u64))
>>>> +
>>>>  struct regs_dump {
>>>>  	u64 abi;
>>>>  	u64 mask;
>>>>  	u64 *regs;
>>>>  
>>>>  	/* Cached values/mask filled by first register access. */
>>>> -	u64 cache_regs[PERF_REGS_MAX];
>>>> +	u64 cache_regs[PERF_SAMPLE_REGS_CACHE_SIZE];
>>>>  	u64 cache_mask;
>>>>  };
>>>>  
>>>> diff --git a/tools/perf/util/perf_regs.c b/tools/perf/util/perf_regs.c
>>>> index 5ee47ae15..06a7461ba 100644
>>>> --- a/tools/perf/util/perf_regs.c
>>>> +++ b/tools/perf/util/perf_regs.c
>>>> @@ -25,6 +25,9 @@ int perf_reg_value(u64 *valp, struct regs_dump *regs, int id)
>>>>  	int i, idx = 0;
>>>>  	u64 mask = regs->mask;
>>>>  
>>>> +	if ((u64)id >= PERF_SAMPLE_REGS_CACHE_SIZE)
>>>> +		return -EINVAL;
>>>> +
>>>>  	if (regs->cache_mask & (1ULL << id))
>>>>  		goto out;
>>>>  
>>>>