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Date:   Fri, 5 Feb 2021 11:34:57 +0100
From:   Borislav Petkov <bp@alien8.de>
To:     Nathan Chancellor <nathan@kernel.org>
Cc:     Ard Biesheuvel <ardb@kernel.org>,
        Arvind Sankar <nivedita@alum.mit.edu>,
        Arnd Bergmann <arnd@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, X86 ML <x86@kernel.org>,
        Nathan Chancellor <natechancellor@gmail.com>,
        Nick Desaulniers <ndesaulniers@google.com>,
        Arnd Bergmann <arnd@arndb.de>,
        Darren Hart <dvhart@infradead.org>,
        Andy Shevchenko <andy@infradead.org>,
        "H. Peter Anvin" <hpa@zytor.com>,
        linux-efi <linux-efi@vger.kernel.org>,
        platform-driver-x86@vger.kernel.org,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        clang-built-linux <clang-built-linux@googlegroups.com>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Subject: Re: [PATCH] x86: efi: avoid BUILD_BUG_ON() for non-constant p4d_index
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On Wed, Feb 03, 2021 at 11:51:48AM -0700, Nathan Chancellor wrote:
> x86_64 all{mod,yes}config with clang are going to ship broken in 5.11.

Dunno, it is still broken here even with those build assertions removed. And it
ain't even an all{mod,yes}config - just my machine's config with

CONFIG_ARCH_HAS_UBSAN_SANITIZE_ALL=y
CONFIG_UBSAN=y
# CONFIG_UBSAN_TRAP is not set
CONFIG_CC_HAS_UBSAN_BOUNDS=y
CONFIG_CC_HAS_UBSAN_ARRAY_BOUNDS=y
CONFIG_UBSAN_BOUNDS=y
CONFIG_UBSAN_ARRAY_BOUNDS=y
CONFIG_UBSAN_SHIFT=y
CONFIG_UBSAN_DIV_ZERO=y
CONFIG_UBSAN_SIGNED_OVERFLOW=y
CONFIG_UBSAN_UNSIGNED_OVERFLOW=y
CONFIG_UBSAN_OBJECT_SIZE=y
CONFIG_UBSAN_BOOL=y
CONFIG_UBSAN_ENUM=y
CONFIG_UBSAN_ALIGNMENT=y
CONFIG_UBSAN_SANITIZE_ALL=y
# CONFIG_TEST_UBSAN is not set

and clang-10:

lib/strncpy_from_user.o: warning: objtool: strncpy_from_user()+0x253: call to __ubsan_handle_add_overflow() with UACCESS enabled
lib/strnlen_user.o: warning: objtool: strnlen_user()+0x244: call to __ubsan_handle_add_overflow() with UACCESS enabled
ld: init/main.o: in function `kmalloc':
/home/boris/kernel/linux/./include/linux/slab.h:557: undefined reference to `__ubsan_handle_alignment_assumption'
ld: init/initramfs.o: in function `kmalloc':
/home/boris/kernel/linux/./include/linux/slab.h:552: undefined reference to `__ubsan_handle_alignment_assumption'
ld: init/initramfs.o: in function `kmalloc_large':
/home/boris/kernel/linux/./include/linux/slab.h:481: undefined reference to `__ubsan_handle_alignment_assumption'
ld: init/initramfs.o: in function `kmalloc':
/home/boris/kernel/linux/./include/linux/slab.h:552: undefined reference to `__ubsan_handle_alignment_assumption'
ld: /home/boris/kernel/linux/./include/linux/slab.h:552: undefined reference to `__ubsan_handle_alignment_assumption'
ld: init/initramfs.o:/home/boris/kernel/linux/./include/linux/slab.h:552: more undefined references to `__ubsan_handle_alignment_assumption' follow
ld: mm/mremap.o: in function `get_extent':
/home/boris/kernel/linux/mm/mremap.c:355: undefined reference to `__compiletime_assert_327'
ld: mm/rmap.o: in function `anon_vma_chain_alloc':
/home/boris/kernel/linux/mm/rmap.c:136: undefined reference to `__ubsan_handle_alignment_assumption'
ld: mm/rmap.o: in function `anon_vma_alloc':
/home/boris/kernel/linux/mm/rmap.c:89: undefined reference to `__ubsan_handle_alignment_assumption'
ld: mm/rmap.o: in function `anon_vma_chain_alloc':
/home/boris/kernel/linux/mm/rmap.c:136: undefined reference to `__ubsan_handle_alignment_assumption'
ld: /home/boris/kernel/linux/mm/rmap.c:136: undefined reference to `__ubsan_handle_alignment_assumption'
ld: /home/boris/kernel/linux/mm/rmap.c:136: undefined reference to `__ubsan_handle_alignment_assumption'
ld: mm/vmalloc.o:/home/boris/kernel/linux/mm/vmalloc.c:1213: more undefined references to `__ubsan_handle_alignment_assumption' follow
make: *** [Makefile:1164: vmlinux] Error 1

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette