linux-kernel - Re: [kvm-unit-tests patch v6 05/18] x86: pmu: Enlarge cnt[] length to 48 in check_counters

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Message-ID: <Z6-wbu7KFqFDLTLH@google.com>
Date: Fri, 14 Feb 2025 13:06:54 -0800
From: Sean Christopherson <seanjc@...gle.com>
To: Dapeng Mi <dapeng1.mi@...ux.intel.com>
Cc: Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Jim Mattson <jmattson@...gle.com>, Mingwei Zhang <mizhang@...gle.com>, 
	Xiong Zhang <xiong.y.zhang@...el.com>, Zhenyu Wang <zhenyuw@...ux.intel.com>, 
	Like Xu <like.xu.linux@...il.com>, Jinrong Liang <cloudliang@...cent.com>, 
	Yongwei Ma <yongwei.ma@...el.com>, Dapeng Mi <dapeng1.mi@...el.com>
Subject: Re: [kvm-unit-tests patch v6 05/18] x86: pmu: Enlarge cnt[] length to
 48 in check_counters_many()

On Sat, Sep 14, 2024, Dapeng Mi wrote:
> Considering there are already 8 GP counters and 4 fixed counters on
> latest Intel processors, like Sapphire Rapids. The original cnt[] array
> length 10 is definitely not enough to cover all supported PMU counters on
> these new processors even through currently KVM only supports 3 fixed
> counters at most. This would cause out of bound memory access and may trigger
> false alarm on PMU counter validation
> 
> It's probably more and more GP and fixed counters are introduced in the
> future and then directly extends the cnt[] array length to 48 once and
> for all. Base on the layout of IA32_PERF_GLOBAL_CTRL and
> IA32_PERF_GLOBAL_STATUS, 48 looks enough in near feature.
> 
> Reviewed-by: Jim Mattson <jmattson@...gle.com>
> Signed-off-by: Dapeng Mi <dapeng1.mi@...ux.intel.com>
> ---
>  x86/pmu.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/x86/pmu.c b/x86/pmu.c
> index a0268db8..b4de2680 100644
> --- a/x86/pmu.c
> +++ b/x86/pmu.c
> @@ -255,7 +255,7 @@ static void check_fixed_counters(void)
>  
>  static void check_counters_many(void)
>  {
> -	pmu_counter_t cnt[10];
> +	pmu_counter_t cnt[48];

ARGH.  Since the *entire* purpose of increasing the size is to guard against
buffer overflow, add an assert that the loop doesn't overflow.

>  	int i, n;
>  
>  	for (i = 0, n = 0; n < pmu.nr_gp_counters; i++) {
> -- 
> 2.40.1
>