From: Josh Poimboeuf <jpoimboe@redhat.com>
To: Jann Horn <jannh@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
Andrew Morton <akpm@linux-foundation.org>,
syzbot <syzbot+ca95b2b7aef9e7cbd6ab@syzkaller.appspotmail.com>,
"H. Peter Anvin" <hpa@zytor.com>,
x86@kernel.org, linux-kernel@vger.kernel.org,
Masahiro Yamada <yamada.masahiro@socionext.com>,
Michal Marek <michal.lkml@markovi.net>,
linux-kbuild@vger.kernel.org
Subject: Re: [PATCH 2/2] x86/unwind: add hardcoded ORC entry for NULL
Date: Fri, 1 Mar 2019 10:24:18 -0600 [thread overview]
Message-ID: <20190301162418.sbhth5tycd6znxin@treble> (raw)
In-Reply-To: <20190301031201.7416-2-jannh@google.com>
On Fri, Mar 01, 2019 at 04:12:01AM +0100, Jann Horn wrote:
> When the ORC unwinder is invoked for an oops caused by IP==0,
> it currently has no idea what to do because there is no debug information
> for the stack frame of NULL.
>
> But if RIP is NULL, it is very likely that the last successfully executed
> instruction was an indirect CALL/JMP, and it is possible to unwind out in
> the same way as for the first instruction of a normal function. Hardcode
> a corresponding ORC entry.
>
>
> With an artificially-added NULL call in prctl_set_seccomp(), before this
> patch, the trace is:
>
> Call Trace:
> ? __x64_sys_prctl+0x402/0x680
> ? __ia32_sys_prctl+0x6e0/0x6e0
> ? __do_page_fault+0x457/0x620
> ? do_syscall_64+0x6d/0x160
> ? entry_SYSCALL_64_after_hwframe+0x44/0xa9
>
> After this patch, the trace looks like this:
>
> Call Trace:
> __x64_sys_prctl+0x402/0x680
> ? __ia32_sys_prctl+0x6e0/0x6e0
> ? __do_page_fault+0x457/0x620
> do_syscall_64+0x6d/0x160
> entry_SYSCALL_64_after_hwframe+0x44/0xa9
>
> prctl_set_seccomp() still doesn't show up in the trace because for some
> reason, tail call optimization is only disabled in builds that use the
> frame pointer unwinder.
>
> Signed-off-by: Jann Horn <jannh@google.com>
Thanks for the patches!
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
> Is there a reason why the top-level Makefile only sets
> -fno-optimize-sibling-calls if CONFIG_FRAME_POINTER is set?
> I suspect that this is just a historical thing, because reliable
> unwinding didn't work without frame pointers until ORC came along.
> I'm not quite sure how best to express "don't do tail optimization if
> either frame pointers are used or ORC is used" in a Makefile, and
> whether we want an indirection through Kconfig for that, so I'm not
> doing anything about it in this series.
> Can someone send a patch to deal with it properly?
Why would sibling calls be a problem for ORC? Once a function does a
sibling call, it has effectively returned and shouldn't show up on the
stack trace anyway.
--
Josh
next prev parent reply other threads:[~2019-03-01 16:26 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-03-01 3:12 [PATCH 1/2] x86/unwind: handle NULL pointer calls better in frame unwinder Jann Horn
2019-03-01 3:12 ` [PATCH 2/2] x86/unwind: add hardcoded ORC entry for NULL Jann Horn
2019-03-01 16:24 ` Josh Poimboeuf [this message]
2019-03-01 16:29 ` Josh Poimboeuf
2019-03-01 16:55 ` Jann Horn
2019-03-01 4:22 ` [PATCH 1/2] x86/unwind: handle NULL pointer calls better in frame unwinder Josh Poimboeuf
2019-03-01 15:32 ` Sean Christopherson
2019-03-01 15:59 ` Jann Horn
2019-03-01 16:19 ` Josh Poimboeuf
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