linux-kernel - Re: [PATCH 00/21] objtool: vmlinux.o and CLANG LTO support

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Date:   Thu, 14 Jan 2021 16:41:28 -0800
From:   Sami Tolvanen <samitolvanen@...gle.com>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     X86 ML <x86@...nel.org>, LKML <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Sedat Dilek <sedat.dilek@...il.com>,
        Kees Cook <keescook@...omium.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        Miroslav Benes <mbenes@...e.cz>
Subject: Re: [PATCH 00/21] objtool: vmlinux.o and CLANG LTO support

Hi Josh,

On Thu, Jan 14, 2021 at 11:40 AM Josh Poimboeuf <jpoimboe@...hat.com> wrote:
>
> Add support for proper vmlinux.o validation, which will be needed for
> Sami's upcoming x86 LTO set.  (And vmlinux validation is the future for
> objtool anyway, for other reasons.)
>
> This isn't 100% done -- most notably, crypto still needs to be supported
> -- but I think this gets us most of the way there.
>
> This can also be found at
>
>   git://git.kernel.org/pub/scm/linux/kernel/git/jpoimboe/linux.git objtool-vmlinux
>
> And for more testing it can be combined with Sami's x86 LTO patches:
>
>   https://github.com/samitolvanen/linux clang-lto

Thank you for sending these! I applied this series on top of the
clang-lto tree and built allyesconfig with LTO_CLANG enabled and the
following crypto options disabled:

CRYPTO_AES_NI_INTEL
CRYPTO_CAMELLIA_AESNI_AVX2_X86_64
CRYPTO_SHA1_SSSE3
CRYPTO_SHA256_SSSE3
CRYPTO_SHA512_SSSE3
CRYPTO_CRC32C_INTEL

I can confirm that all the warnings I previously saw are now fixed,
but I'm seeing a few new ones:

vmlinux.o: warning: objtool: balance_leaf_when_delete()+0x17d4: stack
state mismatch: cfa1=7+192 cfa2=7+176
vmlinux.o: warning: objtool: internal_move_pointers_items()+0x9f7:
stack state mismatch: cfa1=7+160 cfa2=7+176
vmlinux.o: warning: objtool: strncpy_from_user()+0x181: call to
do_strncpy_from_user() with UACCESS enabled
vmlinux.o: warning: objtool: strnlen_user()+0x12b: call to
do_strnlen_user() with UACCESS enabled
vmlinux.o: warning: objtool: i915_gem_execbuffer2_ioctl()+0x390: call
to __ubsan_handle_negate_overflow() with UACCESS enabled
vmlinux.o: warning: objtool: .text.snd_trident_free_voice: unexpected
end of section

I haven't had a chance to take a closer look yet, but some of these
are probably related to
https://github.com/ClangBuiltLinux/linux/issues/1192. However, I can
reproduce these also with ToT Clang, not just with Clang 11.

Sami