From: Borislav Petkov <bp@alien8.de>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
kbuild test robot <fengguang.wu@intel.com>,
Ingo Molnar <mingo@kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
LKML <linux-kernel@vger.kernel.org>,
the arch/x86 maintainers <x86@kernel.org>
Subject: Re: [linus:master] BUILD REGRESSION a2e5790d841658485d642196dbb0927303d6c22f
Date: Wed, 7 Feb 2018 20:28:16 +0100 [thread overview]
Message-ID: <20180207192816.GA19536@pd.tnic> (raw)
In-Reply-To: <20180207191451.GC25201@hirez.programming.kicks-ass.net>
On Wed, Feb 07, 2018 at 08:14:51PM +0100, Peter Zijlstra wrote:
> Then someone went and wrecked it.
Yeah, note says UD0 didn't eat a ModRM byte on old CPUs. But then that
changed too. Fun stuff changing insn encoding underway.
So if we opt for adding a ModRM byte, could a 0x90 NOP work so that it
doesn't shit itself on those old CPUs?
/me goes and checks
Well, no:
b3: 0f ff eb ud0 %ebx,%ebp
decoded with latest objdump turns into:
b3: 0f .byte 0xf
b4: ff .byte 0xff
b5: 90 nop
because 0x90, when used as a ModRM means, AFAICT, register-indirect
addressing with a 32-bit offset which would need more bytes. :-\
/me adds more bytes...
Yap, yuck, that works:
b3: 0f ff 90 90 90 90 90 ud0 -0x6f6f6f70(%rax),%edx
I guess we need to experiment a bit to find a suitable byte to add...
Nasty.
--
Regards/Gruss,
Boris.
Good mailing practices for 400: avoid top-posting and trim the reply.
next prev parent reply other threads:[~2018-02-07 19:28 UTC|newest]
Thread overview: 35+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-02-07 11:44 [linus:master] BUILD REGRESSION a2e5790d841658485d642196dbb0927303d6c22f kbuild test robot
2018-02-07 18:13 ` Linus Torvalds
2018-02-07 18:35 ` Borislav Petkov
2018-02-07 18:49 ` Peter Zijlstra
2018-02-07 19:03 ` Linus Torvalds
2018-02-07 19:14 ` Peter Zijlstra
2018-02-07 19:28 ` Borislav Petkov [this message]
2018-02-07 19:43 ` Linus Torvalds
2018-02-07 20:24 ` Borislav Petkov
2018-02-08 9:13 ` Peter Zijlstra
2018-02-08 9:35 ` Peter Zijlstra
2018-02-08 9:46 ` Borislav Petkov
2018-02-08 9:47 ` David Laight
2018-02-08 10:13 ` Peter Zijlstra
2018-02-08 17:27 ` Linus Torvalds
2018-02-08 18:03 ` Peter Zijlstra
2018-02-08 18:15 ` Linus Torvalds
2018-02-08 19:44 ` Peter Zijlstra
2018-02-08 20:02 ` Linus Torvalds
2018-02-08 20:31 ` Borislav Petkov
2018-02-08 23:09 ` [PATCH 0/2] objtool fixes on top of Peter's WARN UD2 patch Josh Poimboeuf
2018-02-08 23:09 ` [PATCH 1/2] objtool: Fix seg fault in ignore_unreachable_insn() Josh Poimboeuf
2018-02-13 11:29 ` [tip:x86/pti] objtool: Fix segfault " tip-bot for Josh Poimboeuf
2018-02-15 0:26 ` tip-bot for Josh Poimboeuf
2018-02-08 23:09 ` [PATCH 2/2] x86: Annotate WARN-related UD2 as reachable Josh Poimboeuf
2018-02-13 11:30 ` [tip:x86/pti] x86/debug, objtool: Annotate WARN()-related " tip-bot for Josh Poimboeuf
2018-02-15 0:26 ` tip-bot for Josh Poimboeuf
2018-02-09 8:13 ` [PATCH 0/2] objtool fixes on top of Peter's WARN UD2 patch Peter Zijlstra
2018-02-09 8:12 ` [linus:master] BUILD REGRESSION a2e5790d841658485d642196dbb0927303d6c22f Peter Zijlstra
2018-02-13 11:30 ` [tip:x86/pti] x86/debug: Use UD2 for WARN() tip-bot for Peter Zijlstra
2018-02-15 0:27 ` tip-bot for Peter Zijlstra
2018-02-07 18:38 ` [linus:master] BUILD REGRESSION a2e5790d841658485d642196dbb0927303d6c22f Randy Dunlap
2018-02-07 19:01 ` Linus Torvalds
2018-02-07 19:06 ` Peter Zijlstra
2018-02-07 19:10 ` Peter Zijlstra
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