linux-kernel - Re: [PATCH] arm64: Fix KASAN random tag seed initialization

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Message-ID: <CA+fCnZfk5cAO5hC+EJmmvjZRmFRX5A0QScNXScyfajgeKhOSdg@mail.gmail.com>
Date: Wed, 14 Aug 2024 18:04:09 +0200
From: Andrey Konovalov <andreyknvl@...il.com>
To: Samuel Holland <samuel.holland@...ive.com>
Cc: linux-arm-kernel@...ts.infradead.org, 
	Andrew Morton <akpm@...ux-foundation.org>, Ard Biesheuvel <ardb@...nel.org>, 
	Catalin Marinas <catalin.marinas@....com>, Douglas Anderson <dianders@...omium.org>, 
	Frederic Weisbecker <frederic@...nel.org>, James Morse <james.morse@....com>, 
	Jonathan Cameron <Jonathan.Cameron@...wei.com>, Mark Rutland <mark.rutland@....com>, 
	Puranjay Mohan <puranjay@...nel.org>, "Russell King (Oracle)" <rmk+kernel@...linux.org.uk>, 
	Ryo Takakura <takakura@...inux.co.jp>, Shaoqin Huang <shahuang@...hat.com>, 
	Stephen Boyd <swboyd@...omium.org>, Thomas Gleixner <tglx@...utronix.de>, Will Deacon <will@...nel.org>, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] arm64: Fix KASAN random tag seed initialization

On Wed, Aug 14, 2024 at 11:10 AM Samuel Holland
<samuel.holland@...ive.com> wrote:
>
> Currently, kasan_init_sw_tags() is called before setup_per_cpu_areas(),
> so per_cpu(prng_state, cpu) accesses the same address regardless of the
> value of "cpu", and the same seed value gets copied to the percpu area
> for every CPU. Fix this by moving the call to smp_prepare_boot_cpu(),
> which is the first architecture hook after setup_per_cpu_areas().
>
> Fixes: 3c9e3aa11094 ("kasan: add tag related helper functions")
> Fixes: 3f41b6093823 ("kasan: fix random seed generation for tag-based mode")
> Signed-off-by: Samuel Holland <samuel.holland@...ive.com>
> ---
>
>  arch/arm64/kernel/setup.c | 3 ---
>  arch/arm64/kernel/smp.c   | 2 ++
>  2 files changed, 2 insertions(+), 3 deletions(-)
>
> diff --git a/arch/arm64/kernel/setup.c b/arch/arm64/kernel/setup.c
> index a096e2451044..b22d28ec8028 100644
> --- a/arch/arm64/kernel/setup.c
> +++ b/arch/arm64/kernel/setup.c
> @@ -355,9 +355,6 @@ void __init __no_sanitize_address setup_arch(char **cmdline_p)
>         smp_init_cpus();
>         smp_build_mpidr_hash();
>
> -       /* Init percpu seeds for random tags after cpus are set up. */
> -       kasan_init_sw_tags();
> -
>  #ifdef CONFIG_ARM64_SW_TTBR0_PAN
>         /*
>          * Make sure init_thread_info.ttbr0 always generates translation
> diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
> index 5e18fbcee9a2..f01f0fd7b7fe 100644
> --- a/arch/arm64/kernel/smp.c
> +++ b/arch/arm64/kernel/smp.c
> @@ -467,6 +467,8 @@ void __init smp_prepare_boot_cpu(void)
>                 init_gic_priority_masking();
>
>         kasan_init_hw_tags();
> +       /* Init percpu seeds for random tags after cpus are set up. */
> +       kasan_init_sw_tags();
>  }
>
>  /*
> --
> 2.45.1
>

Reviewed-by: Andrey Konovalov <andreyknvl@...il.com>

Thank you!