linux-kernel - Re: [RFC PATCH 0/2] x86: kprobes: Fix CFI

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Message-ID: <20230710155703.GA4021842@dev-arch.thelio-3990X>
Date:   Mon, 10 Jul 2023 08:57:03 -0700
From:   Nathan Chancellor <nathan@...nel.org>
To:     "Masami Hiramatsu (Google)" <mhiramat@...nel.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Petr Pavlu <petr.pavlu@...e.com>, tglx@...utronix.de,
        mingo@...hat.com, bp@...en8.de, dave.hansen@...ux.intel.com,
        hpa@...or.com, samitolvanen@...gle.com, x86@...nel.org,
        linux-trace-kernel@...r.kernel.org, linux-kernel@...r.kernel.org,
        llvm@...ts.linux.dev, ndesaulniers@...gle.com
Subject: Re: [RFC PATCH 0/2] x86: kprobes: Fix CFI_CLANG related issues

On Mon, Jul 10, 2023 at 09:14:13PM +0900, Masami Hiramatsu (Google) wrote:
> I just build tested, since I could not boot the kernel with CFI_CLANG=y.
> Would anyone know something about this error?
> 
> [    0.141030] MMIO Stale Data: Unknown: No mitigations
> [    0.153511] SMP alternatives: Using kCFI
> [    0.164593] Freeing SMP alternatives memory: 36K
> [    0.165053] Kernel panic - not syncing: stack-protector: Kernel stack is corrupted in: start_kernel+0x472/0x48b
> [    0.166028] CPU: 0 PID: 0 Comm: swapper/0 Not tainted 6.4.2-00002-g12b1b2fca8ef #126
> [    0.166028] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.13.0-1ubuntu1.1 04/01/2014
> [    0.166028] Call Trace:
> [    0.166028]  <TASK>
> [    0.166028]  dump_stack_lvl+0x6e/0xb0
> [    0.166028]  panic+0x146/0x2f0
> [    0.166028]  ? start_kernel+0x472/0x48b
> [    0.166028]  __stack_chk_fail+0x14/0x20
> [    0.166028]  start_kernel+0x472/0x48b
> [    0.166028]  x86_64_start_reservations+0x24/0x30
> [    0.166028]  x86_64_start_kernel+0xa6/0xbb
> [    0.166028]  secondary_startup_64_no_verify+0x106/0x11b
> [    0.166028]  </TASK>
> [    0.166028] ---[ end Kernel panic - not syncing: stack-protector: Kernel stack is corrupted in: start_kernel+0x472/0x48b ]---

This looks like https://github.com/ClangBuiltLinux/linux/issues/1815 to
me. What version of LLVM are you using? This was fixed in 16.0.4. Commit
514ca14ed544 ("start_kernel: Add __no_stack_protector function
attribute") should resolve it on the Linux side, it looks like that is
in 6.5-rc1. Not sure if we should backport it or just let people upgrade
their toolchains on older releases.

Cheers,
Nathan