linux-kernel - Re: [PATCH] perf annotate: Fix memcpy size in arch__grow

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Message-ID: <CAP-5=fVOeYCU_6ukDi_3g=H=K5HXoN+UjcNCysEbCO3LAY3ukw@mail.gmail.com>
Date: Thu, 22 Jan 2026 10:27:27 -0800
From: Ian Rogers <irogers@...gle.com>
To: Suchit Karunakaran <suchitkarunakaran@...il.com>
Cc: acme@...nel.org, mingo@...hat.com, namhyung@...nel.org, 
	peterz@...radead.org, adrian.hunter@...el.com, 
	alexander.shishkin@...ux.intel.com, james.clark@...aro.org, jolsa@...nel.org, 
	mark.rutland@....com, linux-perf-users@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] perf annotate: Fix memcpy size in arch__grow_instructions

On Thu, Jan 22, 2026 at 9:17 AM Suchit Karunakaran
<suchitkarunakaran@...il.com> wrote:
>
> The memcpy in arch__grow_instructions() is copying the wrong number of
> bytes when growing from a non-allocated table. It should copy
> arch->nr_instructions * sizeof(struct ins) bytes, not just
> arch->nr_instructions bytes.
>
> This bug causes data corruption as only a partial copy of the
> instruction table is made, leading to garbage data in most entries and
> potential crashes
>
> Signed-off-by: Suchit Karunakaran <suchitkarunakaran@...il.com>
> ---
>  tools/perf/util/disasm.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/tools/perf/util/disasm.c b/tools/perf/util/disasm.c
> index 50b9433f3f8e..6faa9df8e373 100644
> --- a/tools/perf/util/disasm.c
> +++ b/tools/perf/util/disasm.c
> @@ -81,7 +81,7 @@ static int arch__grow_instructions(struct arch *arch)
>         if (new_instructions == NULL)
>                 return -1;
>
> -       memcpy(new_instructions, arch->instructions, arch->nr_instructions);
> +       memcpy(new_instructions, arch->instructions, arch->nr_instructions * sizeof(struct ins));

Reviewed-by: Ian Rogers <irogers@...gle.com>

Nice catch! I think we've been trying to make code like this more like:
memcpy(new_instructions, arch->instructions, arch->nr_instructions *
sizeof(*new_instructions));
but the immediately preceding calloc isn't doing this, so your patch
is consistent. There is also a clean up in this code to switch to
using reallocarray rather than realloc.

Thanks,
Ian

>         goto out_update_instructions;
>  }
>
> --
> 2.52.0
>