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Message-ID: <20220715032333.neywlazczbb35w3b@treble> Date: Thu, 14 Jul 2022 20:23:33 -0700 From: Josh Poimboeuf <jpoimboe@...nel.org> To: Peter Zijlstra <peterz@...radead.org> Cc: Kees Cook <keescook@...omium.org>, kernel test robot <oliver.sang@...el.com>, x86@...nel.org, Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>, "H. Peter Anvin" <hpa@...or.com>, Arnd Bergmann <arnd@...db.de>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org Subject: Re: [PATCH] x86: Allow for exclusions in checking RETHUNK On Thu, Jul 14, 2022 at 11:56:07AM -0700, Josh Poimboeuf wrote: > On Thu, Jul 14, 2022 at 11:50:08AM -0700, Josh Poimboeuf wrote: > > On Thu, Jul 14, 2022 at 09:18:12AM +0200, Peter Zijlstra wrote: > > > On Wed, Jul 13, 2022 at 04:55:56PM -0700, Josh Poimboeuf wrote: > > > > Here's the ANNOTATE_UNSAFE_RET idea. > > > > > > Right, I suppose that strictly speaking the compiler can do whatever and > > > there's no actual guarantee the annotation hits the RET instruction, in > > > practise it should work, esp. since noinstr. > > > > Hm, KASAN is introducing a weird function, resulting in a naked return > > warning since we have RETHUNK_CFLAGS removed on that file. > > > > 0000000000000000 <_sub_I_00099_0>: > > 0: e8 00 00 00 00 call 5 <_sub_I_00099_0+0x5> 1: R_X86_64_PLT32 __tsan_init-0x4 > > 5: c3 ret > > > > > > Looks like the "KASAN_SANITIZE_rodata.o := n" isn't working somehow? > > Oh never mind, I got KASAN/KCSCAN mixed up. Needs both disabled :-/ Well, my ANNOTATE_UNSAFE_RET trick didn't quite work either, as it results in .discard.retpoline_safe pointing to .rodata when IBT is enabled. Instead I'll just do OBJECT_FILES_NON_STANDARD_rodata.o. That shouldn't break LTO/IBT because the linked code lives in .rodata anyway. Will have patches tomorrow, if they pass bot testing. -- Josh
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