Re: [PATCH v2 5/9] riscv: mm: Log potential KASAN shadow alias

From: Alexandre Ghiti <alex@ghiti.fr>
To: Samuel Holland <samuel.holland@sifive.com>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	linux-riscv@lists.infradead.org,
	Andrey Ryabinin <ryabinin.a.a@gmail.com>,
	Alexander Potapenko <glider@google.com>,
	Andrey Konovalov <andreyknvl@gmail.com>,
	Dmitry Vyukov <dvyukov@google.com>,
	Vincenzo Frascino <vincenzo.frascino@arm.com>,
	kasan-dev@googlegroups.com
Cc: llvm@lists.linux.dev, Catalin Marinas <catalin.marinas@arm.com>,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	Alexandre Ghiti <alexghiti@rivosinc.com>,
	Will Deacon <will@kernel.org>,
	Evgenii Stepanov <eugenis@google.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v2 5/9] riscv: mm: Log potential KASAN shadow alias
Date: Tue, 5 Nov 2024 14:44:25 +0100	[thread overview]
Message-ID: <5dba5a49-91e5-4988-9018-63b146b5e26c@ghiti.fr> (raw)
In-Reply-To: <20241022015913.3524425-6-samuel.holland@sifive.com>

Hi Samuel,

On 22/10/2024 03:57, Samuel Holland wrote:
> When KASAN is enabled, shadow memory is allocated and mapped for all
> legitimate kernel addresses, but not for the entire address space. As a
> result, the kernel can fault when accessing a shadow address computed
> from a bogus pointer. This can be confusing, because the shadow address
> computed for (e.g.) NULL looks nothing like a NULL pointer. To assist
> debugging, if the faulting address might be the result of a KASAN shadow
> memory address computation, report the range of original memory
> addresses that would map to the faulting address.
>
> Signed-off-by: Samuel Holland <samuel.holland@sifive.com>
> ---
>
> Changes in v2:
>   - New patch for v2
>
>   arch/riscv/mm/fault.c | 3 +++
>   1 file changed, 3 insertions(+)
>
> diff --git a/arch/riscv/mm/fault.c b/arch/riscv/mm/fault.c
> index a9f2b4af8f3f..dae1131221b7 100644
> --- a/arch/riscv/mm/fault.c
> +++ b/arch/riscv/mm/fault.c
> @@ -8,6 +8,7 @@
>   
>   
>   #include <linux/mm.h>
> +#include <linux/kasan.h>
>   #include <linux/kernel.h>
>   #include <linux/interrupt.h>
>   #include <linux/perf_event.h>
> @@ -30,6 +31,8 @@ static void die_kernel_fault(const char *msg, unsigned long addr,
>   	pr_alert("Unable to handle kernel %s at virtual address " REG_FMT "\n", msg,
>   		addr);
>   
> +	kasan_non_canonical_hook(addr);
> +
>   	bust_spinlocks(0);
>   	die(regs, "Oops");
>   	make_task_dead(SIGKILL);

That's nice, I used to do that by hand :)

Reviewed-by: Alexandre Ghiti <alexghiti@rivosinc.com>

Thanks,

Alex