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

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Date: Mon, 29 Apr 2024 10:18:03 -0700
From: Kees Cook <keescook@...omium.org>
To: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>
Cc: Erick Archer <erick.archer@...look.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>,
	"Gustavo A. R. Silva" <gustavoars@...nel.org>, x86@...nel.org,
	linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-hardening@...r.kernel.org
Subject: Re: [PATCH] perf/x86/intel/uncore: Prefer struct_size over open
 coded arithmetic

On Sat, Mar 30, 2024 at 03:32:59PM +0100, 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 "box" variable is a pointer to "struct intel_uncore_box" and
> this structure ends in a flexible array:
> 
> struct intel_uncore_box {
> 	[...]
> 	struct intel_uncore_extra_reg shared_regs[];
> };
> 
> 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_node() function.
> 
> This way, the code is more readable and safer.
> 
> This code was detected with the help of Coccinelle, and audited and
> modified manually.
> 
> 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@...look.com>
> ---
> Hi,
> 
> The Coccinelle script used to detect this code pattern is the following:
> 
> virtual report
> 
> @rule1@
> type t1;
> type t2;
> identifier i0;
> identifier i1;
> identifier i2;
> identifier ALLOC =~ "kmalloc|kzalloc|kmalloc_node|kzalloc_node|vmalloc|vzalloc|kvmalloc|kvzalloc";
> position p1;
> @@
> 
> i0 = sizeof(t1) + sizeof(t2) * i1;
> ...
> i2 = ALLOC@p1(..., i0, ...);
> 
> @script:python depends on report@
> p1 << rule1.p1;
> @@
> 
> msg = "WARNING: verify allocation on line %s" % (p1[0].line)
> coccilib.report.print_report(p1[0],msg)
> 
> Regards,
> Erick
> ---
>  arch/x86/events/intel/uncore.c | 7 +++----
>  1 file changed, 3 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/x86/events/intel/uncore.c b/arch/x86/events/intel/uncore.c
> index 258e2cdf28fa..ce756d24c370 100644
> --- a/arch/x86/events/intel/uncore.c
> +++ b/arch/x86/events/intel/uncore.c
> @@ -350,12 +350,11 @@ static void uncore_pmu_init_hrtimer(struct intel_uncore_box *box)
>  static struct intel_uncore_box *uncore_alloc_box(struct intel_uncore_type *type,
>  						 int node)
>  {
> -	int i, size, numshared = type->num_shared_regs ;
> +	int i, numshared = type->num_shared_regs;
>  	struct intel_uncore_box *box;
>  
> -	size = sizeof(*box) + numshared * sizeof(struct intel_uncore_extra_reg);
> -
> -	box = kzalloc_node(size, GFP_KERNEL, node);
> +	box = kzalloc_node(struct_size(box, shared_regs, numshared), GFP_KERNEL,
> +			   node);
>  	if (!box)
>  		return NULL;

Thanks, yes, this looks correct to me.

Reviewed-by: Kees Cook <keescook@...omium.org>

Peter and Ingo, you seem to traditionally take these changes (via -tip)?
Can you please pick this up?

-- 
Kees Cook