From: Dave Martin <Dave.Martin@arm.com>
To: Mark Brown <broonie@kernel.org>
Cc: Tamas Zsoldos <tamas.zsoldos@arm.com>,
Will Deacon <will@kernel.org>,
kernel-team@android.com, linux-arm-kernel@lists.infradead.org,
Daniel Kiss <daniel.kiss@arm.com>
Subject: Re: [PATCH 1/3] arm64: vdso: Don't prefix sigreturn trampoline with a BTI C instruction
Date: Tue, 19 May 2020 15:55:15 +0100 [thread overview]
Message-ID: <20200519145514.GH5031@arm.com> (raw)
In-Reply-To: <20200519143500.GK4611@sirena.org.uk>
On Tue, May 19, 2020 at 03:35:00PM +0100, Mark Brown wrote:
> On Tue, May 19, 2020 at 02:25:38PM +0100, Dave Martin wrote:
>
> > Rather, the "ret lr" that jumps here is supposed to be authenticated via
> > pointer auth in the caller.
>
> In which case there was an issue anyway...
What issue?
> > If BTI {nothing} allows this while disallowing all BR/BLR then we could
> > use that (I can't remember what BTI {nothing} is useful for, if anything).
>
> > Otherwise, it's less clear what we should have here.
>
> I can't remember anything that distinguishes it from an explicit NOP.
I think it rejects everything other then fallthrough execution
(BTYPE==0, which includes RET). I might have misunderstood something
somewhere, but sort of feels like the right thing here. I never put a
lot of effort into trying to understand BTI {nothing} though. It
seemed a weird, possibly useless special case.
Of course, if gdb's unwinder does rely on recognising magic instruction
sequences in the sigreturn trampoline even when the vdso has valid
unwind information, we're probably doomed to stick for the current code
forever.
Cheers
---Dave
_______________________________________________
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:[~2020-05-19 14:55 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-19 12:18 [PATCH 0/3] arm64 sigreturn unwinding fixes Will Deacon
2020-05-19 12:18 ` [PATCH 1/3] arm64: vdso: Don't prefix sigreturn trampoline with a BTI C instruction Will Deacon
2020-05-19 12:38 ` Mark Brown
2020-05-19 13:25 ` Dave Martin
2020-05-19 14:35 ` Mark Brown
2020-05-19 14:55 ` Dave Martin [this message]
2020-05-19 15:42 ` Mark Brown
2020-05-20 9:48 ` Dave Martin
2020-05-20 10:46 ` Mark Brown
2020-05-20 11:08 ` Dave Martin
2020-05-19 15:26 ` Will Deacon
2020-05-19 13:21 ` Dave Martin
2020-05-19 13:29 ` Will Deacon
2020-05-19 12:18 ` [PATCH 2/3] arm64: vdso: Add a comment to justify the mysterious NOP in sigreturn Will Deacon
2020-05-19 13:26 ` Dave Martin
2020-05-19 12:18 ` [PATCH 3/3] arm64: vdso: Fix CFI directives in sigreturn trampoline Will Deacon
2020-05-19 13:09 ` Dave P Martin
2020-05-19 13:39 ` Will Deacon
2020-05-19 13:55 ` Dave Martin
2020-05-19 15:24 ` Will Deacon
2020-05-19 15:30 ` Daniel Kiss
2020-05-19 15:55 ` Will Deacon
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=20200519145514.GH5031@arm.com \
--to=dave.martin@arm.com \
--cc=broonie@kernel.org \
--cc=daniel.kiss@arm.com \
--cc=kernel-team@android.com \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=tamas.zsoldos@arm.com \
--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).