From: Catalin Marinas <catalin.marinas@arm.com>
To: Jens Axboe <axboe@kernel.dk>
Cc: Will Deacon <will@kernel.org>, linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH] arm64: treat PF_IO_WORKER like PF_KTHREAD for mitigations
Date: Thu, 26 Jan 2023 15:04:27 +0000 [thread overview]
Message-ID: <Y9KWeyy9tAKYDxGA@arm.com> (raw)
In-Reply-To: <012e38c7-8cb9-a65c-a553-e8a2fafe6f3b@kernel.dk>
On Thu, Jan 26, 2023 at 07:07:45AM -0700, Jens Axboe wrote:
> On 1/26/23 7:00 AM, Will Deacon wrote:
> > On Wed, Jan 25, 2023 at 09:43:34AM -0700, Jens Axboe wrote:
> >> Like PF_KTHREAD, PF_IO_WORKER never exit to userspace. They exist
> >> entirely within the kernel, and hence don't need any task mitigations
> >> applied.
> >>
> >> Signed-off-by: Jens Axboe <axboe@kernel.dk>
> >>
> >> ---
> >>
> >> diff --git a/arch/arm64/kernel/proton-pack.c b/arch/arm64/kernel/proton-pack.c
> >> index fca9cc6f5581..25a21c3d446c 100644
> >> --- a/arch/arm64/kernel/proton-pack.c
> >> +++ b/arch/arm64/kernel/proton-pack.c
> >> @@ -654,7 +654,7 @@ static void __update_pstate_ssbs(struct pt_regs *regs, bool state)
> >> void spectre_v4_enable_task_mitigation(struct task_struct *tsk)
> >> {
> >> struct pt_regs *regs = task_pt_regs(tsk);
> >> - bool ssbs = false, kthread = tsk->flags & PF_KTHREAD;
> >> + bool ssbs = false, kthread = tsk->flags & (PF_KTHREAD | PF_IO_WORKER);
> >
> > Hmm, the other two uses of PF_KTHREAD in arch/arm64 also look pretty
> > suspect in light of this proposal. Should we also update
> > ssbs_thread_switch() and access_ok()? If not, then a comment would be
> > handy to say why PF_KTHREAD is sufficient there.
>
> The uaccess one looks like, PF_IO_WORKER threads are just normal userspace
> threads. The only difference is that they never exit to userspace, they
> remain in the kernel. But everything else is just like a thread.
IIUC these threads are cloned from a user thread and inherit the TIF
flags. If the user already opted in to the tagged addr ABI (usually
early by libc), TIF_TAGGED_ADDR would be set for all threads and
inherited by io_worker threads so we get away with this. But it doesn't
hurt to extend the access_ok check to PF_IO_WORKER just in case the user
plays with the late enabling of TIF_TAGGED_ADDR.
--
Catalin
_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
next prev parent reply other threads:[~2023-01-26 15:06 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-01-25 16:43 [PATCH] arm64: treat PF_IO_WORKER like PF_KTHREAD for mitigations Jens Axboe
2023-01-26 14:00 ` Will Deacon
2023-01-26 14:07 ` Jens Axboe
2023-01-26 15:04 ` Catalin Marinas [this message]
2023-03-28 14:14 ` Will Deacon
2023-03-28 16:47 ` Jens Axboe
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=Y9KWeyy9tAKYDxGA@arm.com \
--to=catalin.marinas@arm.com \
--cc=axboe@kernel.dk \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=will@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).