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References: <20221202135149.1797974-1-colin.i.king@gmail.com>
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From:   Ian Rogers <irogers@google.com>
Date:   Fri, 2 Dec 2022 09:36:14 -0800
Message-ID: <CAP-5=fWKbC_wOLiAnEnPV42mM9fpobJD++wKohFYVU66LdaJ-g@mail.gmail.com>
Subject: Re: [PATCH][next] perf/x86/amd: fix potential integer overflow on
 shift of a int
To:     Colin Ian King <colin.i.king@gmail.com>
Cc:     Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Jiri Olsa <jolsa@kernel.org>,
        Namhyung Kim <namhyung@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Borislav Petkov <bp@alien8.de>,
        Dave Hansen <dave.hansen@linux.intel.com>, x86@kernel.org,
        "H . Peter Anvin" <hpa@zytor.com>,
        Kim Phillips <kim.phillips@amd.com>,
        linux-perf-users@vger.kernel.org, kernel-janitors@vger.kernel.org,
        linux-kernel@vger.kernel.org
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On Fri, Dec 2, 2022 at 5:52 AM Colin Ian King <colin.i.king@gmail.com> wrote:
>
> The left shift of int 32 bit integer constant 1 is evaluated using 32 bit
> arithmetic and then passed as a 64 bit function argument. In the case where
> i is 32 or more this can lead to an overflow.  Avoid this by shifting
> using the BIT_ULL macro instead.
>
> Fixes: 471af006a747 ("perf/x86/amd: Constrain Large Increment per Cycle events")
> Signed-off-by: Colin Ian King <colin.i.king@gmail.com>

Acked-by: Ian Rogers <irogers@google.com>

Thanks,
Ian

> ---
>  arch/x86/events/amd/core.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/x86/events/amd/core.c b/arch/x86/events/amd/core.c
> index d6f3703e4119..4386b10682ce 100644
> --- a/arch/x86/events/amd/core.c
> +++ b/arch/x86/events/amd/core.c
> @@ -1387,7 +1387,7 @@ static int __init amd_core_pmu_init(void)
>                  * numbered counter following it.
>                  */
>                 for (i = 0; i < x86_pmu.num_counters - 1; i += 2)
> -                       even_ctr_mask |= 1 << i;
> +                       even_ctr_mask |= BIT_ULL(i);
>
>                 pair_constraint = (struct event_constraint)
>                                     __EVENT_CONSTRAINT(0, even_ctr_mask, 0,
> --
> 2.38.1
>