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AArch64 BTI support - No BTI after setjmp #48888

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llvmbot opened this issue Mar 11, 2021 · 16 comments
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AArch64 BTI support - No BTI after setjmp #48888

llvmbot opened this issue Mar 11, 2021 · 16 comments
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@tstellar
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backend:AArch64 bugzilla Issues migrated from bugzilla confirmed Verified by a second party release:backport release:cherry-pick-failed release:reviewed
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LLVM 14.0.2 Release

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@llvmbot
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llvmbot commented Mar 11, 2021

Bugzilla Link 49544
Version 11.0
OS other
Reporter LLVM Bugzilla Contributor
CC @DougGregor,@zygoloid,@smithp35

Extended Description

When enabling the -mbranch-protection={bti,standard} option in Clang, BTI/PAC instruction are well inserted at each function entry, which works well.
However, the setjmp/longjmp API is not supported while it is in the GNU GCC compiler (see https://gcc.gnu.org/legacy-ml/gcc-patches/2018-11/msg02472.html).
To work properly, a BTI instruction must be added after each call to setjmp function. I have not found any reference to similar in Clang.

While this code is under fixing, is it possible to build a Clang/LLVM module to add instruction right after these setjmp calls ?
@smithp35
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As I understand it there is a trade off between adding a BTI after a call to setjmp which permits setjmp to return with an indirect jump, but also means there are more gadgets in the program, the address in the jump_buf could be retrieved and branched to.

For example the Bionic implementation of longjump returns with a ret which means a BTI is not needed https://android.googlesource.com/platform/bionic/+/refs/heads/master/libc/arch-arm64/bionic/setjmp.S

Having said that, if the compiler doesn't know what libc is being used it should assume that it might need a BTI and insert one after setjmp. If it does happen to know, such as when Android is used, then it won't need to.

So I agree we should do this. I couldn't give you a commitment of when it will happen though.

@llvmbot llvmbot transferred this issue from llvm/llvm-bugzilla-archive Dec 11, 2021
@DavidSpickett
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I've just started to look at doing this. https://reviews.llvm.org/D112427 did the same thing for Arm 32 bit M profile targets so I will base it on that. Then we can have the clang side drivers set it if we know what that platform's C lib does.

Showing the difference: https://godbolt.org/z/PzMhvo6WM

@llvmbot
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llvmbot commented Jan 10, 2022

@llvm/issue-subscribers-backend-AArch64

@llvmbot llvmbot added the confirmed Verified by a second party label Jan 26, 2022
tom-cosgrove-arm added a commit to tom-cosgrove-arm/openssl that referenced this issue Feb 14, 2022
@tom-cosgrove-arm
aarch64: Fix async_fibre_swapcontext() on clang BTI builds
4d056f2 
Reverting to using swapcontext() when compiling with clang on BTI-enabled
builds fixes the BTI setjmp() failure seen when running asynctest.

The issue with setjmp/longjmp is a known clang bug: see
llvm/llvm-project#48888

Change-Id: I6eeaaa2e15f402789f1b3e742038f84bef846e29
@tom-cosgrove-arm tom-cosgrove-arm mentioned this issue Feb 14, 2022
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openssl-machine pushed a commit to openssl/openssl that referenced this issue Feb 28, 2022
@tom-cosgrove-arm @paulidale
aarch64: Fix async_fibre_swapcontext() on clang BTI builds
f5ec705 
Reverting to using swapcontext() when compiling with clang on BTI-enabled
builds fixes the BTI setjmp() failure seen when running asynctest.

The issue with setjmp/longjmp is a known clang bug: see
llvm/llvm-project#48888

Change-Id: I6eeaaa2e15f402789f1b3e742038f84bef846e29

Reviewed-by: Matt Caswell <matt@openssl.org>
Reviewed-by: Paul Dale <pauli@openssl.org>
(Merged from #17698)

(cherry picked from commit d2d2401)
openssl-machine pushed a commit to openssl/openssl that referenced this issue Feb 28, 2022
@tom-cosgrove-arm @paulidale
aarch64: Fix async_fibre_swapcontext() on clang BTI builds
d2d2401 
Reverting to using swapcontext() when compiling with clang on BTI-enabled
builds fixes the BTI setjmp() failure seen when running asynctest.

The issue with setjmp/longjmp is a known clang bug: see
llvm/llvm-project#48888

Change-Id: I6eeaaa2e15f402789f1b3e742038f84bef846e29

Reviewed-by: Matt Caswell <matt@openssl.org>
Reviewed-by: Paul Dale <pauli@openssl.org>
(Merged from #17698)
@DavidSpickett DavidSpickett changed the title ARM BTI support - No BTI after setjmp AArch64 BTI support - No BTI after setjmp Mar 14, 2022
@DavidSpickett
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OP-TEE workaround for future reference: OP-TEE/optee_os@30e743f

I now have a working patch just need to see how to add GlobalIsel support as well.

@DavidSpickett
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https://reviews.llvm.org/D121707

@EugeneZelenko EugeneZelenko removed the c label Mar 23, 2022
@DavidSpickett
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This has landed on main, I will request a backport to 14 tomorrow if the buildbots don't bring up anything else.

@DavidSpickett DavidSpickett reopened this Mar 24, 2022
@DavidSpickett DavidSpickett added this to the LLVM 14.0.1 Release milestone Mar 24, 2022
@DavidSpickett
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/cherry-pick c3b9819

@llvmbot
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llvmbot commented Mar 24, 2022

Failed to cherry-pick: c3b9819

https://github.com/llvm/llvm-project/actions/runs/2033442748

Please manually backport the fix and push it to your github fork. Once this is done, please add a comment like this:

/branch <user>/<repo>/<branch>

@DavidSpickett
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/branch DavidSpickett/llvm-project/setjmp-bti-llvm-14

@llvmbot llvmbot mentioned this issue Mar 24, 2022
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@llvmbot
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llvmbot commented Mar 24, 2022

/pull-request llvmbot#132

@tstellar
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tstellar commented Apr 2, 2022

@TNorthover What do you think about backporting this? c3b9819

@TNorthover
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I think it looks OK.

@TNorthover TNorthover assigned tstellar and unassigned TNorthover Apr 7, 2022
@tstellar
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@DavidSpickett Can you rebase your branch.

@DavidSpickett
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Done.

@DavidSpickett
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I see the change on 14.x now so I've removed it from main's release notes 218b5c8.

@DavidSpickett
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Closing now that this has gone into 14.0.2.

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Labels
backend:AArch64 bugzilla Issues migrated from bugzilla confirmed Verified by a second party release:backport release:cherry-pick-failed release:reviewed
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@tstellar @DavidSpickett @TNorthover @EugeneZelenko @kbeyls @smithp35 @llvmbot