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From: Sami Tolvanen <samitolvanen@google.com>
To: Josh Poimboeuf <jpoimboe@redhat.com>,
	Nick Desaulniers <ndesaulniers@google.com>
Cc: Sedat Dilek <sedat.dilek@gmail.com>, X86 ML <x86@kernel.org>,
	LKML <linux-kernel@vger.kernel.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Kees Cook <keescook@chromium.org>,
	Clang-Built-Linux ML <clang-built-linux@googlegroups.com>,
	Miroslav Benes <mbenes@suse.cz>
Subject: Re: [PATCH v2 00/20] objtool: vmlinux.o and CLANG LTO support
Date: Fri, 22 Jan 2021 13:17:28 -0800	[thread overview]
Message-ID: <CABCJKueaW1BEEBKLQzyp77VwTL+bE4x=kOLV3TWmc1s6-r3PeQ@mail.gmail.com> (raw)
In-Reply-To: <20210122154158.lylubqugmcxehugg@treble>

Hi Josh,

On Fri, Jan 22, 2021 at 7:42 AM Josh Poimboeuf <jpoimboe@redhat.com> wrote:
>
> On Thu, Jan 21, 2021 at 11:38:54PM +0100, Sedat Dilek wrote:
> > On Thu, Jan 21, 2021 at 10:29 PM Josh Poimboeuf <jpoimboe@redhat.com> wrote:
> > >
> > > v2:
> > > - fix commit description for why xen hypervisor page contents don't
> > >   matter [Juergen]
> > > - annotate indirect jumps as safe instead of converting them to
> > >   retpolines [Andrew, Juergen]
> > > - drop patch 1 - fake jumps no longer exist
> > > - add acks
> > >
> > > Based on tip/objtool/core.
> > >
> > >
> > > 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
> > >
> >
> > Should this be s/objtool-vmlinux/objtool-vmlinux-v2 ?
>
> Indeed:
>
>   git://git.kernel.org/pub/scm/linux/kernel/git/jpoimboe/linux.git objtool-vmlinux-v2

I tested v2 on top of the LTO tree and with allyesconfig + relevant
crypto configs disabled, and I only see the warnings I reported
earlier.

I also tested this on top of the CFI tree and with LTO+CFI enabled, I
can reproduce the segfault Sedat reported in the previous thread. This
happens because find_unsuffixed_func is called with a NULL sym in
read_relocs:

Program received signal SIGSEGV, Segmentation fault.
find_unsuffixed_func (elf=elf@entry=0x7ffff55a5010, sym=0x0,
suffix=0x416cbf ".cfi_jt", func=func@entry=0x7fffffffd5f0) at
elf.c:274
274             loc = strstr(sym->name, suffix);
(gdb) bt
#0  find_unsuffixed_func (elf=elf@entry=0x7ffff55a5010, sym=0x0,
suffix=0x416cbf ".cfi_jt", func=func@entry=0x7fffffffd5f0) at
elf.c:274
#1  0x000000000040d8f8 in read_relocs (elf=0x7ffff55a5010) at elf.c:637
...

In this specific case, find_func_by_offset returns NULL for
.text..L.cfi.jumptable.43 at addend 0x8, because Clang doesn't emit
jump table symbols for static functions:

0000000000000000 <__typeid__ZTSFjmiE_global_addr>:
   0:   e9 00 00 00 00          jmpq   5 <__typeid__ZTSFjmiE_global_addr+0x5>
                        1: R_X86_64_PLT32       io_serial_in-0x4
   5:   cc                      int3
   6:   cc                      int3
   7:   cc                      int3
   8:   e9 00 00 00 00          jmpq   d <__typeid__ZTSFjmiE_global_addr+0xd>
                        9: R_X86_64_PLT32       mem32_serial_in-0x4
   d:   cc                      int3
   e:   cc                      int3
   f:   cc                      int3

Nick, do you remember if there were plans to change this?

Sami

  reply	other threads:[~2021-01-22 21:19 UTC|newest]

Thread overview: 31+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-01-21 21:29 [PATCH v2 00/20] objtool: vmlinux.o and CLANG LTO support Josh Poimboeuf
2021-01-21 21:29 ` [PATCH v2 01/20] objtool: Fix error handling for STD/CLD warnings Josh Poimboeuf
2021-01-21 21:29 ` [PATCH v2 02/20] objtool: Fix retpoline detection in asm code Josh Poimboeuf
2021-01-21 21:29 ` [PATCH v2 03/20] objtool: Fix ".cold" section suffix check for newer versions of GCC Josh Poimboeuf
2021-01-21 21:29 ` [PATCH v2 04/20] objtool: Support retpoline jump detection for vmlinux.o Josh Poimboeuf
2021-01-21 21:29 ` [PATCH v2 05/20] x86/ftrace: Add UNWIND_HINT_FUNC annotation for ftrace_stub Josh Poimboeuf
2021-01-21 21:29 ` [PATCH v2 06/20] objtool: Assume only ELF functions do sibling calls Josh Poimboeuf
2021-01-21 21:29 ` [PATCH v2 07/20] objtool: Add asm version of STACK_FRAME_NON_STANDARD Josh Poimboeuf
2021-01-21 21:29 ` [PATCH v2 08/20] objtool: Combine UNWIND_HINT_RET_OFFSET and UNWIND_HINT_FUNC Josh Poimboeuf
2021-01-21 21:29 ` [PATCH v2 09/20] objtool: Add xen_start_kernel() to noreturn list Josh Poimboeuf
2021-01-21 21:29 ` [PATCH v2 10/20] objtool: Move unsuffixed symbol conversion to a helper function Josh Poimboeuf
2021-01-21 21:29 ` [PATCH v2 11/20] objtool: Add CONFIG_CFI_CLANG support Josh Poimboeuf
2021-01-21 21:29 ` [PATCH v2 12/20] x86/xen: Support objtool validation in xen-asm.S Josh Poimboeuf
2021-01-21 21:29 ` [PATCH v2 13/20] x86/xen: Support objtool vmlinux.o validation in xen-head.S Josh Poimboeuf
2021-01-21 21:29 ` [PATCH v2 14/20] x86/xen/pvh: Annotate indirect branch as safe Josh Poimboeuf
2021-01-22  5:17   ` Jürgen Groß
2021-01-21 21:29 ` [PATCH v2 15/20] x86/ftrace: Support objtool vmlinux.o validation in ftrace_64.S Josh Poimboeuf
2021-01-21 21:29 ` [PATCH v2 16/20] x86/acpi: Annotate indirect branch as safe Josh Poimboeuf
2021-01-21 21:29 ` [PATCH v2 17/20] x86/acpi: Support objtool validation in wakeup_64.S Josh Poimboeuf
2021-01-21 21:29 ` [PATCH v2 18/20] x86/power: Annotate indirect branches as safe Josh Poimboeuf
2021-01-21 21:29 ` [PATCH v2 19/20] x86/power: Move restore_registers() to top of the file Josh Poimboeuf
2021-01-21 21:29 ` [PATCH v2 20/20] x86/power: Support objtool validation in hibernate_asm_64.S Josh Poimboeuf
2021-01-21 22:38 ` [PATCH v2 00/20] objtool: vmlinux.o and CLANG LTO support Sedat Dilek
2021-01-22 15:41   ` Josh Poimboeuf
2021-01-22 21:17     ` Sami Tolvanen [this message]
2021-01-23  1:32       ` Nick Desaulniers
2021-01-23  2:26         ` Josh Poimboeuf
2021-01-23  2:31           ` Sedat Dilek
2021-01-23  2:46             ` Josh Poimboeuf
2021-01-23  2:50               ` Sedat Dilek
2021-01-25 22:43           ` Sami Tolvanen

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