From: Andrew Cooper <Andrew.Cooper3@citrix.com>
To: David Laight <David.Laight@ACULAB.COM>,
Peter Zijlstra <peterz@infradead.org>,
"x86@kernel.org" <x86@kernel.org>,
"joao@overdrivepizza.com" <joao@overdrivepizza.com>,
"hjl.tools@gmail.com" <hjl.tools@gmail.com>,
"jpoimboe@redhat.com" <jpoimboe@redhat.com>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"ndesaulniers@google.com" <ndesaulniers@google.com>,
"keescook@chromium.org" <keescook@chromium.org>,
"samitolvanen@google.com" <samitolvanen@google.com>,
"mark.rutland@arm.com" <mark.rutland@arm.com>,
"alyssa.milburn@intel.com" <alyssa.milburn@intel.com>,
Andrew Cooper <Andrew.Cooper3@citrix.com>
Subject: Re: [PATCH 05/29] x86: Base IBT bits
Date: Fri, 18 Feb 2022 21:24:10 +0000 [thread overview]
Message-ID: <c7fa2998-0532-b46c-7bfb-ed41620f10b8@citrix.com> (raw)
In-Reply-To: <bf7f2867a77e4ebe8c44fd0577a3ac55@AcuMS.aculab.com>
On 18/02/2022 21:11, David Laight wrote:
> From: Andrew Cooper
>> Sent: 18 February 2022 20:50
>>
>> On 18/02/2022 16:49, Peter Zijlstra wrote:
>>> +/*
>>> + * A bit convoluted, but matches both endbr32 and endbr64 without
>>> + * having either as literal in the text.
>>> + */
>>> +static inline bool is_endbr(const void *addr)
>>> +{
>>> + unsigned int val = ~*(unsigned int *)addr;
>>> + val |= 0x01000000U;
>>> + return val == ~0xfa1e0ff3;
>>> +}
>> At this point, I feel I've earned an "I told you so". :)
>>
>> Clang 13 sees straight through the trickery and generates:
>>
>> is_endbr: # @is_endbr
>> movl $-16777217, %eax # imm = 0xFEFFFFFF
>> andl (%rdi), %eax
>> cmpl $-98693133, %eax # imm = 0xFA1E0FF3
>> sete %al
>> retq
> I think it is enough to add:
> asm("", "=r" (val));
> somewhere in the middle.
(First, you mean "+r" not "=r"), but no - the problem isn't val. It's
`~0xfa1e0ff3` which the compiler is free to transform in several unsafe way.
~Andrew
next prev parent reply other threads:[~2022-02-18 21:24 UTC|newest]
Thread overview: 94+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-02-18 16:49 [PATCH 00/29] x86: Kernel IBT Peter Zijlstra
2022-02-18 16:49 ` [PATCH 01/29] static_call: Avoid building empty .static_call_sites Peter Zijlstra
2022-02-18 16:49 ` [PATCH 02/29] x86/module: Fix the paravirt vs alternative order Peter Zijlstra
2022-02-18 20:28 ` Josh Poimboeuf
2022-02-18 21:22 ` Peter Zijlstra
2022-02-18 23:28 ` Josh Poimboeuf
2022-02-18 16:49 ` [PATCH 03/29] objtool: Add --dry-run Peter Zijlstra
2022-02-18 16:49 ` [PATCH 04/29] x86/livepatch: Validate __fentry__ location Peter Zijlstra
2022-02-18 21:08 ` Josh Poimboeuf
2022-02-23 10:09 ` Peter Zijlstra
2022-02-23 10:21 ` Miroslav Benes
2022-02-23 10:57 ` Peter Zijlstra
2022-02-23 12:41 ` Steven Rostedt
2022-02-23 14:05 ` Peter Zijlstra
2022-02-23 14:16 ` Steven Rostedt
2022-02-23 14:23 ` Steven Rostedt
2022-02-23 14:33 ` Steven Rostedt
2022-02-23 14:49 ` Peter Zijlstra
2022-02-23 15:54 ` Peter Zijlstra
2022-02-18 16:49 ` [PATCH 05/29] x86: Base IBT bits Peter Zijlstra
2022-02-18 20:49 ` Andrew Cooper
2022-02-18 21:11 ` David Laight
2022-02-18 21:24 ` Andrew Cooper [this message]
2022-02-18 22:37 ` David Laight
2022-02-18 21:26 ` Peter Zijlstra
2022-02-18 21:14 ` Josh Poimboeuf
2022-02-18 21:21 ` Peter Zijlstra
2022-02-18 22:12 ` Joao Moreira
2022-02-19 1:07 ` Edgecombe, Rick P
2022-02-18 16:49 ` [PATCH 06/29] x86/ibt: Add ANNOTATE_NOENDBR Peter Zijlstra
2022-02-18 16:49 ` [PATCH 07/29] x86/entry: Sprinkle ENDBR dust Peter Zijlstra
2022-02-19 0:23 ` Josh Poimboeuf
2022-02-19 23:08 ` Peter Zijlstra
2022-02-19 0:36 ` Josh Poimboeuf
2022-02-18 16:49 ` [PATCH 08/29] x86/linkage: Add ENDBR to SYM_FUNC_START*() Peter Zijlstra
2022-02-18 16:49 ` [PATCH 09/29] x86/ibt,paravirt: Sprinkle ENDBR Peter Zijlstra
2022-02-18 16:49 ` [PATCH 10/29] x86/bpf: Add ENDBR instructions to prologue Peter Zijlstra
2022-02-18 16:49 ` [PATCH 11/29] x86/ibt,crypto: Add ENDBR for the jump-table entries Peter Zijlstra
2022-02-18 16:49 ` [PATCH 12/29] x86/ibt,kvm: Add ENDBR to fastops Peter Zijlstra
2022-02-18 16:49 ` [PATCH 13/29] x86/ibt,ftrace: Add ENDBR to samples/ftrace Peter Zijlstra
2022-02-18 16:49 ` [PATCH 14/29] x86/ibt: Add IBT feature, MSR and #CP handling Peter Zijlstra
2022-02-18 19:31 ` Andrew Cooper
2022-02-18 21:15 ` Peter Zijlstra
2022-02-19 1:20 ` Edgecombe, Rick P
2022-02-19 1:21 ` Josh Poimboeuf
2022-02-19 9:24 ` Peter Zijlstra
2022-02-21 8:24 ` Kees Cook
2022-02-22 4:38 ` Edgecombe, Rick P
2022-02-22 9:32 ` Peter Zijlstra
2022-02-18 16:49 ` [PATCH 15/29] x86: Disable IBT around firmware Peter Zijlstra
2022-02-21 8:27 ` Kees Cook
2022-02-21 10:06 ` Peter Zijlstra
2022-02-21 13:22 ` Peter Zijlstra
2022-02-21 15:54 ` Kees Cook
2022-02-21 16:10 ` Peter Zijlstra
2022-02-18 16:49 ` [PATCH 16/29] x86/bugs: Disable Retpoline when IBT Peter Zijlstra
2022-02-19 2:15 ` Josh Poimboeuf
2022-02-22 15:00 ` Peter Zijlstra
2022-02-25 0:19 ` Josh Poimboeuf
2022-02-18 16:49 ` [PATCH 17/29] x86/ibt: Annotate text references Peter Zijlstra
2022-02-19 5:22 ` Josh Poimboeuf
2022-02-19 9:39 ` Peter Zijlstra
2022-02-18 16:49 ` [PATCH 18/29] x86/ibt,ftrace: Annotate ftrace code patching Peter Zijlstra
2022-02-18 16:49 ` [PATCH 19/29] x86/ibt,xen: Annotate away warnings Peter Zijlstra
2022-02-18 20:24 ` Andrew Cooper
2022-02-18 21:05 ` Peter Zijlstra
2022-02-18 23:07 ` Andrew Cooper
2022-02-21 14:20 ` Peter Zijlstra
2022-02-18 16:49 ` [PATCH 20/29] x86/ibt,sev: Annotations Peter Zijlstra
2022-02-18 16:49 ` [PATCH 21/29] objtool: Rename --duplicate to --lto Peter Zijlstra
2022-02-26 19:42 ` Josh Poimboeuf
2022-02-26 21:48 ` Josh Poimboeuf
2022-02-28 11:05 ` Peter Zijlstra
2022-02-28 18:32 ` Josh Poimboeuf
2022-02-28 20:09 ` Peter Zijlstra
2022-02-28 20:18 ` Josh Poimboeuf
2022-03-01 14:19 ` Miroslav Benes
2022-02-18 16:49 ` [PATCH 22/29] Kbuild: Prepare !CLANG whole module objtool Peter Zijlstra
2022-02-18 16:49 ` [PATCH 23/29] objtool: Read the NOENDBR annotation Peter Zijlstra
2022-02-18 16:49 ` [PATCH 24/29] x86/text-patching: Make text_gen_insn() IBT aware Peter Zijlstra
2022-02-24 1:18 ` Joao Moreira
2022-02-24 9:10 ` Peter Zijlstra
2022-02-18 16:49 ` [PATCH 25/29] x86/ibt: Dont generate ENDBR in .discard.text Peter Zijlstra
2022-02-18 16:49 ` [PATCH 26/29] objtool: Add IBT validation / fixups Peter Zijlstra
2022-02-18 16:49 ` [PATCH 27/29] x86/ibt: Finish --ibt-fix-direct on module loading Peter Zijlstra
2022-02-18 16:49 ` [PATCH 28/29] x86/ibt: Ensure module init/exit points have references Peter Zijlstra
2022-02-18 16:49 ` [PATCH 29/29] x86/alternative: Use .ibt_endbr_sites to seal indirect calls Peter Zijlstra
2022-02-19 1:29 ` [PATCH 00/29] x86: Kernel IBT Edgecombe, Rick P
2022-02-19 9:58 ` Peter Zijlstra
2022-02-19 16:00 ` Andrew Cooper
2022-02-21 8:42 ` Kees Cook
2022-02-21 9:24 ` Peter Zijlstra
2022-02-23 7:26 ` Kees Cook
2022-02-24 16:47 ` Mike Rapoport
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