linux-hardening - Re: [PATCH] perf/x86/rapl: Prefer struct

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Date: Sun, 17 Mar 2024 14:14:02 -0600
From: "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To: Erick Archer <erick.archer@....com>, Peter Zijlstra
 <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>,
 Arnaldo Carvalho de Melo <acme@...nel.org>,
 Namhyung Kim <namhyung@...nel.org>, Mark Rutland <mark.rutland@....com>,
 Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
 Jiri Olsa <jolsa@...nel.org>, Ian Rogers <irogers@...gle.com>,
 Adrian Hunter <adrian.hunter@...el.com>, Thomas Gleixner
 <tglx@...utronix.de>, Borislav Petkov <bp@...en8.de>,
 Dave Hansen <dave.hansen@...ux.intel.com>, "H. Peter Anvin" <hpa@...or.com>,
 Kees Cook <keescook@...omium.org>,
 "Gustavo A. R. Silva" <gustavoars@...nel.org>
Cc: x86@...nel.org, linux-perf-users@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH] perf/x86/rapl: Prefer struct_size over open coded
 arithmetic

On 3/17/24 10:44, Erick Archer wrote:
> This is an effort to get rid of all multiplications from allocation
> functions in order to prevent integer overflows [1][2].
> 
> As the "rapl_pmus" variable is a pointer to "struct rapl_pmus" and
> this structure ends in a flexible array:
> 
> struct rapl_pmus {
> 	[...]
> 	struct rapl_pmu *pmus[] __counted_by(maxdie);
> };
> 
> the preferred way in the kernel is to use the struct_size() helper to
> do the arithmetic instead of the calculation "size + count * size" in
> the kzalloc() function.
> 
> This way, the code is more readable and safer.
> 
> Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#open-coded-arithmetic-in-allocator-arguments [1]
> Link: https://github.com/KSPP/linux/issues/160 [2]
> Signed-off-by: Erick Archer <erick.archer@....com>
LGTM:

Reviewed-by: Gustavo A. R. Silva <gustavoars@...nel.org>

Thanks!
--
Gustavo

> ---
>   arch/x86/events/rapl.c | 4 +---
>   1 file changed, 1 insertion(+), 3 deletions(-)
> 
> diff --git a/arch/x86/events/rapl.c b/arch/x86/events/rapl.c
> index fb2b1961e5a3..8ef08b5d55a7 100644
> --- a/arch/x86/events/rapl.c
> +++ b/arch/x86/events/rapl.c
> @@ -675,10 +675,8 @@ static const struct attribute_group *rapl_attr_update[] = {
>   static int __init init_rapl_pmus(void)
>   {
>   	int maxdie = topology_max_packages() * topology_max_dies_per_package();
> -	size_t size;
> 
> -	size = sizeof(*rapl_pmus) + maxdie * sizeof(struct rapl_pmu *);
> -	rapl_pmus = kzalloc(size, GFP_KERNEL);
> +	rapl_pmus = kzalloc(struct_size(rapl_pmus, pmus, maxdie), GFP_KERNEL);
>   	if (!rapl_pmus)
>   		return -ENOMEM;
> 
> --
> 2.25.1
> 
>