From: Nathan Chancellor <natechancellor@gmail.com>
To: Will Deacon <will@kernel.org>
Cc: mark.rutland@arm.com, tstellar@redhat.com,
android-kvm@google.com, catalin.marinas@arm.com,
ndesaulniers@google.com, clang-built-linux@googlegroups.com,
Mark Brown <broonie@kernel.org>,
linux-arm-kernel@lists.infradead.org, daniel.kiss@arm.com
Subject: Re: Clang miscompiling arm64 kernel with BTI and PAC?
Date: Mon, 15 Jun 2020 07:31:05 -0700 [thread overview]
Message-ID: <20200615143105.GA2283265@ubuntu-n2-xlarge-x86> (raw)
In-Reply-To: <20200615120223.GC2694@willie-the-truck>
[+ Tom, the clang 10 release manager]
On Mon, Jun 15, 2020 at 01:02:23PM +0100, Will Deacon wrote:
> On Mon, Jun 15, 2020 at 12:53:37PM +0100, Mark Brown wrote:
> > On Mon, Jun 15, 2020 at 11:55:24AM +0100, Will Deacon wrote:
> >
> > > Here, the switch statement has been replaced by a jump table which we *tail
> > > call* into. The register dump shows we're going to 0xffffd68929392e14:
> >
> > > ffff800010032e14: d503233f paciasp
> > > ffff800010032e18: a9bf7bfd stp x29, x30, [sp, #-16]!
> > > ffff800010032e1c: 910003fd mov x29, sp
> > > ffff800010032e20: aa0803e0 mov x0, x8
> > > ffff800010032e24: 940017c0 bl ffff800010038d24 <kvm_vm_ioctl_check_extension>
> > > ffff800010032e28: 93407c00 sxtw x0, w0
> > > ffff800010032e2c: a8c17bfd ldp x29, x30, [sp], #16
> > > ffff800010032e30: d50323bf autiasp
> > > ffff800010032e34: d65f03c0 ret
> >
> > > The problem is that the paciasp instruction is not BTYPE-compatible with BR;
> > > it expects to be called with a branch-and-link, and so we panic. I think you
> > > need to emit a 'bti j' here prior to the paciasp.
> >
> > I checked with our internal teams and they actually ran into this
> > recently with some other code, the patch:
> >
> > https://reviews.llvm.org/D81746
> >
> > ([AArch64] Fix BTI instruction emission) should fix this, it's been
> > reviewed so should be merged shortly.
>
> Cheers, that's good to hear. Shall we have a guess at the clang release
> that will get the fix, or just disable in-kernel BTI with clang for now?
>
> Will
>
This will be in clang 11 for sure. Tom, would it be too late to get this
in to clang 10.0.1? If it is not, I can open a PR.
Cheers,
Nathan
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next prev parent reply other threads:[~2020-06-15 14:31 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-15 10:55 Clang miscompiling arm64 kernel with BTI and PAC? Will Deacon
2020-06-15 11:37 ` Mark Brown
2020-06-15 11:53 ` Mark Brown
2020-06-15 12:02 ` Will Deacon
2020-06-15 14:31 ` Nathan Chancellor [this message]
2020-06-15 15:00 ` Daniel Kiss
2020-06-16 17:37 ` Will Deacon
2020-06-16 17:49 ` Nathan Chancellor
2020-06-16 17:55 ` Will Deacon
2020-06-16 18:35 ` Nick Desaulniers
2020-06-17 6:36 ` Fangrui Song
2020-06-18 11:22 ` Daniel Kiss
2020-06-16 18:09 ` Tom Stellard
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