Re: [PATCH] riscv: Disallow PR_GET_TAGGED_ADDR_CTRL without Supm

From: Nam Cao <namcao@linutronix.de>
To: Samuel Holland <samuel.holland@sifive.com>
Cc: Alexandre Ghiti <alex@ghiti.fr>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	linux-riscv@lists.infradead.org,
	Albert Ou <aou@eecs.berkeley.edu>,
	Bill O'Donnell <bodonnel@redhat.com>,
	Charlie Jenkins <charlie@rivosinc.com>,
	Conor Dooley <conor.dooley@microchip.com>,
	Joel Granados <joel.granados@kernel.org>,
	Paul Walmsley <paul.walmsley@sifive.com>,
	Yunhui Cui <cuiyunhui@bytedance.com>,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH] riscv: Disallow PR_GET_TAGGED_ADDR_CTRL without Supm
Date: Wed, 7 May 2025 20:08:11 +0200	[thread overview]
Message-ID: <20250507180811.3CKhxtu0@linutronix.de> (raw)
In-Reply-To: <20250507145230.2272871-1-samuel.holland@sifive.com>

On Wed, May 07, 2025 at 07:52:18AM -0700, Samuel Holland wrote:
> When the prctl() interface for pointer masking was added, it did not
> check that the pointer masking ISA extension was supported, only the
> individual submodes. Userspace could still attempt to disable pointer
> masking and query the pointer masking state. commit 81de1afb2dd1
> ("riscv: Fix kernel crash due to PR_SET_TAGGED_ADDR_CTRL") disallowed
> the former, as the senvcfg write could crash on older systems.
> PR_GET_TAGGED_ADDR_CTRL state does not crash, because it reads only
> kernel-internal state and not senvcfg, but it should still be disallowed
> for consistency.
> 
> Fixes: 09d6775f503b ("riscv: Add support for userspace pointer masking")
> Signed-off-by: Samuel Holland <samuel.holland@sifive.com>
> ---
> 
>  arch/riscv/kernel/process.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/arch/riscv/kernel/process.c b/arch/riscv/kernel/process.c
> index 7c244de77180..f7a1a887ae68 100644
> --- a/arch/riscv/kernel/process.c
> +++ b/arch/riscv/kernel/process.c
> @@ -330,6 +330,9 @@ long get_tagged_addr_ctrl(struct task_struct *task)
>  	struct thread_info *ti = task_thread_info(task);
>  	long ret = 0;
>  
> +	if (!riscv_has_extension_unlikely(RISCV_ISA_EXT_SUPM))
> +		return -EINVAL;
> +
>  	if (is_compat_thread(ti))
>  		return -EINVAL;

I think this matches what the man page says:

"If the arguments are invalid or this feature is disabled or unsupported by
the kernel, the call fails with EINVAL"

Reviewed-by: Nam Cao <namcao@linutronix.de>

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