From: Mark Rutland <mark.rutland@arm.com>
To: Derrick McKee <derrick.mckee@gmail.com>
Cc: Nathan.Burow@ll.mit.edu, Yianni Giannaris <yiannig@mit.edu>,
Catalin Marinas <catalin.marinas@arm.com>,
Will Deacon <will@kernel.org>,
linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH] Ensure kernel AI key is not changed on fork
Date: Thu, 20 May 2021 17:00:35 +0100 [thread overview]
Message-ID: <20210520160035.GP17233@C02TD0UTHF1T.local> (raw)
In-Reply-To: <20210520151854.3632129-1-derrick.mckee@gmail.com>
On Thu, May 20, 2021 at 11:18:54AM -0400, Derrick McKee wrote:
> The kernel uses the IA key for PAC signing,
> and this key should remain unchanged from the kernel point of view.
> This patch ensures that the IA key remains constant on fork,
> if it has been previously set.
> The software is provided on an as-is basis.
>
> Signed-off-by: Derrick McKee <derrick.mckee@gmail.com>
> Signed-off-by: Yianni Giannaris <yiannig@mit.edu>
On the kernel side, we use a unique IA key per kernel thread, and while
this must remain the same *for that kernel thread*, the kernel IA key
should differ across kernel threads when a fork() occurs.
I think you're trying to use the keys in a different way than upstream
intends to, and we do not need this change as-is.
So NAK to this patch as it stands.
Thanks,
Mark.
> ---
> arch/arm64/include/asm/pointer_auth.h | 9 ++++++---
> 1 file changed, 6 insertions(+), 3 deletions(-)
>
> diff --git a/arch/arm64/include/asm/pointer_auth.h b/arch/arm64/include/asm/pointer_auth.h
> index d50416be99be..9748413e72fd 100644
> --- a/arch/arm64/include/asm/pointer_auth.h
> +++ b/arch/arm64/include/asm/pointer_auth.h
> @@ -69,10 +69,13 @@ static inline void ptrauth_keys_init_user(struct ptrauth_keys_user *keys)
> ptrauth_keys_install_user(keys);
> }
>
> -static __always_inline void ptrauth_keys_init_kernel(struct ptrauth_keys_kernel *keys)
> +static __always_inline void
> +ptrauth_keys_init_kernel(struct ptrauth_keys_kernel *keys)
> {
> - if (system_supports_address_auth())
> - get_random_bytes(&keys->apia, sizeof(keys->apia));
> + if (keys->apia.lo == 0 && keys->apia.hi == 0) {
> + if (system_supports_address_auth())
> + get_random_bytes(&keys->apia, sizeof(keys->apia));
> + }
> }
>
> static __always_inline void ptrauth_keys_switch_kernel(struct ptrauth_keys_kernel *keys)
> --
> 2.31.1
>
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next prev parent reply other threads:[~2021-05-20 16:04 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-30 14:40 PAC key changes when kernel code is preempted Derrick McKee
2021-04-30 15:04 ` Mark Rutland
2021-05-07 20:24 ` Derrick McKee
2021-05-20 15:18 ` [PATCH] Ensure kernel AI key is not changed on fork Derrick McKee
2021-05-20 16:00 ` Mark Rutland [this message]
2021-05-20 18:24 ` Derrick McKee
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