From: Joao Moreira <joao@overdrivepizza.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Kees Cook <keescook@chromium.org>,
x86@kernel.org, Sami Tolvanen <samitolvanen@google.com>,
linux-kernel@vger.kernel.org, Mark Rutland <mark.rutland@arm.com>,
Josh Poimboeuf <jpoimboe@redhat.com>
Subject: Re: [PATCH] x86/ibt: Implement FineIBT
Date: Tue, 18 Oct 2022 21:48:42 -0700 [thread overview]
Message-ID: <d219d61420c48a90a2e8bdc29cb8a579@overdrivepizza.com> (raw)
In-Reply-To: <Y08M4+GxoqvuZ+bq@hirez.programming.kicks-ass.net>
>> Is it useful to get the compiler to emit 0xcc with
>> -fpatchable-function-entry under any circumstance? I can probably
>> change
>> that quickly if needed/useful.
>
> Having it emit 0xcc for the bytes in front of the symbol might be
> interesting. It would mean a few kernel changes, but nothing too hard.
>
> That is, -fpatchable-function-entry=N,M gets us N-M bytes in at the
> start of the symbol and M bytes in front of it. The N-M bytes at the
> start of the function *are* executed and should obviously not become
> 0xcc (GCC keeps them 0x90 while LLVM makes them large NOPs).
Uhum, all makes sense. I drafted something here:
https://github.com/lvwr/llvm-project/commits/joao/int3
Let me know if this works for you or if there is something that should
be tweaked, like adding a specific flag and such. This currently emits
0xcc instead of 0x90 for the nops before the function entry symbol for
kernel code on x86-64. It seems to be working (see generated snippet
below), but let me know otherwise:
Generated with -fpatchable-function-entry=10,5
Disassembly of section .text:
0000000000000000 <save_processor_state-0x5>:
0: cc int3
1: cc int3
2: cc int3
3: cc int3
4: cc int3
0000000000000005 <save_processor_state>:
5: 0f 1f 44 00 08 nopl 0x8(%rax,%rax,1)
a: 41 57 push %r15
c: 41 56 push %r14
...
next prev parent reply other threads:[~2022-10-19 4:48 UTC|newest]
Thread overview: 42+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-10-18 13:35 [PATCH] x86/ibt: Implement FineIBT Peter Zijlstra
2022-10-18 14:43 ` David Laight
2022-10-18 15:58 ` Joao Moreira
2022-10-18 17:20 ` Kees Cook
2022-10-18 20:09 ` Joao Moreira
2022-10-19 5:33 ` Kees Cook
2022-10-18 21:27 ` David Laight
2022-10-18 14:47 ` Peter Zijlstra
2022-10-18 18:09 ` Kees Cook
2022-10-18 19:56 ` Peter Zijlstra
2022-10-18 23:31 ` Josh Poimboeuf
2022-10-19 5:22 ` Kees Cook
2022-10-19 11:38 ` Peter Zijlstra
2022-10-19 5:14 ` Kees Cook
2022-10-18 19:59 ` Peter Zijlstra
2022-10-18 21:09 ` Peter Zijlstra
2022-10-19 5:05 ` Kees Cook
2022-10-19 12:03 ` Peter Zijlstra
2022-10-19 15:22 ` Sami Tolvanen
2022-10-20 11:04 ` Peter Zijlstra
2022-10-18 19:59 ` Joao Moreira
2022-10-19 5:32 ` Kees Cook
2022-10-19 19:35 ` Joao Moreira
2022-10-18 20:05 ` Peter Zijlstra
2022-10-19 5:00 ` Kees Cook
2022-10-18 20:09 ` Peter Zijlstra
2022-10-18 20:17 ` Joao Moreira
2022-10-18 20:30 ` Peter Zijlstra
2022-10-19 4:48 ` Joao Moreira [this message]
2022-10-19 5:19 ` Kees Cook
2022-10-31 19:13 ` Joao Moreira
2022-11-01 21:39 ` Kees Cook
2022-11-01 21:50 ` Joao Moreira
2022-10-19 5:18 ` Kees Cook
2022-10-19 5:16 ` Kees Cook
2022-10-20 11:05 ` Peter Zijlstra
2022-10-18 23:38 ` Josh Poimboeuf
2022-10-19 7:29 ` Peter Zijlstra
2022-10-21 23:08 ` Josh Poimboeuf
2022-10-22 15:03 ` Peter Zijlstra
2022-10-24 17:15 ` Sami Tolvanen
2022-10-24 18:38 ` Joao Moreira
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