From: Mark Brown <broonie@kernel.org>
To: Dave Martin <Dave.Martin@arm.com>
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 16:42:47 +0100 [thread overview]
Message-ID: <20200519154247.GN4611@sirena.org.uk> (raw)
In-Reply-To: <20200519145514.GH5031@arm.com>
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On Tue, May 19, 2020 at 03:55:15PM +0100, Dave Martin wrote:
> 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?
None, I was confused.
> > > 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
Right, but since BTI only generates an exception when BTYPE != 0 I'm
having trouble differentiating this from a NOP in practical terms.
> 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.
That was my read too.
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next prev parent reply other threads:[~2020-05-19 15:42 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
2020-05-19 15:42 ` Mark Brown [this message]
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
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