From: Peter Zijlstra <peterz@infradead.org>
To: Kees Cook <keescook@chromium.org>
Cc: x86@kernel.org, Sami Tolvanen <samitolvanen@google.com>,
Joao Moreira <joao@overdrivepizza.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 22:09:23 +0200 [thread overview]
Message-ID: <Y08H8zJ5lQ62jel5@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <202210181020.79AF7F7@keescook>
On Tue, Oct 18, 2022 at 11:09:13AM -0700, Kees Cook wrote:
> > +#ifdef CONFIG_FINEIBT
> > +/*
> > + * kCFI FineIBT
> > + *
> > + * __cfi_\func: __cfi_\func:
> > + * movl $0x12345678,%eax endbr64 // 4
>
> kCFI emits endbr64 here first too ...
>
> > + * nop subl $0x12345678,%r10d // 7
> > + * nop jz 1f // 2
> > + * nop ud2 // 2
> > + * nop 1: nop // 1
> > + * nop
> > + * nop
> > + * nop
> > + * nop
> > + * nop
> > + * nop
> > + * nop
It does not; it does emit ENDBR at the start of the regular symbol
though:
0000000000001040 <__cfi_yield>:
1040: b8 0c 67 40 a5 mov $0xa540670c,%eax
1045: 90 nop
1046: 90 nop
1047: 90 nop
1048: 90 nop
1049: 90 nop
104a: 90 nop
104b: 90 nop
104c: 90 nop
104d: 90 nop
104e: 90 nop
104f: 90 nop
0000000000001050 <yield>:
1050: f3 0f 1e fa endbr64
1054: e8 00 00 00 00 call 1059 <yield+0x9> 1055: R_X86_64_PLT32 __fentry__-0x4
1059: 65 48 8b 05 00 00 00 00 mov %gs:0x0(%rip),%rax # 1061 <yield+0x11> 105d: R_X86_64_PC32 pcpu_hot-0x4
1061: 31 c9 xor %ecx,%ecx
1063: 87 48 18 xchg %ecx,0x18(%rax)
1066: e9 00 00 00 00 jmp 106b <yield+0x1b> 1067: R_X86_64_PLT32 .text+0xc08c
106b: 0f 1f 44 00 00 nopl 0x0(%rax,%rax,1)
Not doing that is an option...
> Tangent: why are these nop instead of 0xcc? These bytes aren't executed
> ever are they?
Because that's what the compiler gets us through -fpatchable-function-entry.
next prev parent reply other threads:[~2022-10-18 20:09 UTC|newest]
Thread overview: 44+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-10-18 13:35 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 [this message]
2022-10-18 20:17 ` Joao Moreira
2022-10-18 20:30 ` Peter Zijlstra
2022-10-19 4:48 ` Joao Moreira
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
2024-05-06 17:36 ` Kees Cook
2024-05-07 1:45 ` 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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