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

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Message-ID: <6705021e-5b02-3323-7dbc-4b774f22a435@linux.ibm.com>
Date:   Fri, 10 Dec 2021 14:47:49 +0530
From:   kajoljain <kjain@...ux.ibm.com>
To:     German Gomez <german.gomez@....com>, linux-kernel@...r.kernel.org,
        linux-perf-users@...r.kernel.org, acme@...nel.org
Cc:     John Garry <john.garry@...wei.com>, Will Deacon <will@...nel.org>,
        Mathieu Poirier <mathieu.poirier@...aro.org>,
        Leo Yan <leo.yan@...aro.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        linux-arm-kernel@...ts.infradead.org, linux-csky@...r.kernel.org,
        linux-riscv@...ts.infradead.org
Subject: Re: [PATCH v1 1/4] perf tools: Prevent out-of-bounds access to
 registers



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@...ux.ibm.com>

Thanks,
Kajol Jain

> Signed-off-by: German Gomez <german.gomez@....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;
>  
>