From: Oleg Nesterov <oleg@redhat.com>
To: Mark Brown <broonie@kernel.org>
Cc: "Edgecombe, Rick P" <rick.p.edgecombe@intel.com>,
"mingo@kernel.org" <mingo@kernel.org>,
"dave.hansen@linux.intel.com" <dave.hansen@linux.intel.com>,
"bp@alien8.de" <bp@alien8.de>,
"peterz@infradead.org" <peterz@infradead.org>,
"hpa@zytor.com" <hpa@zytor.com>,
"axboe@kernel.dk" <axboe@kernel.dk>,
"tglx@linutronix.de" <tglx@linutronix.de>,
"Mehta, Sohil" <sohil.mehta@intel.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"x86@kernel.org" <x86@kernel.org>,
"debug@rivosinc.com" <debug@rivosinc.com>
Subject: Re: [PATCH 5/6] x86/shstk: don't create the shadow stack for PF_USER_WORKERs
Date: Fri, 15 Aug 2025 15:01:26 +0200 [thread overview]
Message-ID: <20250815130125.GD11549@redhat.com> (raw)
In-Reply-To: <e50065a9-d5e2-4e94-94b2-e34c5fac9720@sirena.org.uk>
On 08/14, Mark Brown wrote:
>
> On Thu, Aug 14, 2025 at 05:03:36PM +0000, Edgecombe, Rick P wrote:
> > On Thu, 2025-08-14 at 12:14 +0200, Oleg Nesterov wrote:
>
> > > If a features_enabled(ARCH_SHSTK_SHSTK) userspace thread creates a
> > > PF_USER_WORKER thread, shstk_alloc_thread_stack() allocates the shadow
> > > stack for no reason, the new (kernel) thread will never return to usermode.
>
> > I agree we don't need to allocate a shadow stack in this case, but I'm not sure
> > it is right to fully disable shadow stack in thread.features. First of all,
> > disabling it from shstk_alloc_thread_stack() seems weird. It just handles
> > allocating shadow stacks.
>
> I agree that it's better to leave userspace shadow stacks enabled, given
> that the reason we're not allocating the shadow stack is that we don't
> expect to ever return to userspace then it should be fine to leave the
> feature turned on for userspace. If we mess up and do somehow return to
> userspace
But a PF_USER_WORKER task can never return to userspace. It doesn't differ
from PF_KTHREAD in this respect.
Oleg.
next prev parent reply other threads:[~2025-08-15 13:02 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-08-14 10:13 [PATCH 0/6] x86/fpu: don't abuse x86_task_fpu(PF_USER_WORKER) in .regset_get() paths Oleg Nesterov
2025-08-14 10:14 ` [PATCH 1/6] x86/fpu: change copy_xstate_to_uabi_buf() to accept fpstate + pkru instead of task_struct Oleg Nesterov
2025-08-14 16:46 ` Edgecombe, Rick P
2025-08-15 12:22 ` Oleg Nesterov
2025-08-14 10:14 ` [PATCH 2/6] x86/fpu: regset: introduce get_fpstate() helper Oleg Nesterov
2025-08-14 10:14 ` [PATCH 3/6] x86/fpu: fold sync_fpstate() into get_fpstate() Oleg Nesterov
2025-08-14 10:14 ` [PATCH 4/6] x86/shstk: add "task_struct *tsk" argument to reset_thread_features() Oleg Nesterov
2025-08-14 10:14 ` [PATCH 5/6] x86/shstk: don't create the shadow stack for PF_USER_WORKERs Oleg Nesterov
2025-08-14 17:03 ` Edgecombe, Rick P
2025-08-14 18:33 ` Mark Brown
2025-08-14 22:43 ` Edgecombe, Rick P
2025-08-15 11:44 ` Mark Brown
2025-08-15 19:11 ` Deepak Gupta
2025-08-18 17:27 ` Mark Brown
2025-08-19 17:41 ` Deepak Gupta
2025-08-15 13:01 ` Oleg Nesterov [this message]
2025-08-15 13:08 ` Oleg Nesterov
2025-08-15 15:28 ` Mark Brown
2025-08-15 15:43 ` Oleg Nesterov
2025-08-15 15:48 ` Mark Brown
2025-08-15 16:00 ` Oleg Nesterov
2025-08-15 17:08 ` Mark Brown
2025-08-15 12:17 ` Oleg Nesterov
2025-08-15 16:19 ` Edgecombe, Rick P
2025-08-15 16:54 ` Oleg Nesterov
2025-08-15 17:46 ` Edgecombe, Rick P
2025-08-15 19:13 ` Oleg Nesterov
2025-08-14 10:14 ` [PATCH 6/6] x86/fpu: change get_fpstate() to return &init_fpstate if PF_USER_WORKER Oleg Nesterov
2025-08-15 15:52 ` [PATCH 0/6] x86/fpu: don't abuse x86_task_fpu(PF_USER_WORKER) in .regset_get() paths Oleg Nesterov
2025-08-15 15:59 ` Dave Hansen
2025-08-15 16:02 ` Oleg Nesterov
2025-08-15 16:32 ` Sohil Mehta
2025-08-15 19:33 ` Oleg Nesterov
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