From: David Woodhouse <dwmw2@infradead.org>
To: Borislav Petkov <bp@suse.de>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>,
"tglx@linutronix.de" <tglx@linutronix.de>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"tim.c.chen@linux.intel.com" <tim.c.chen@linux.intel.com>,
"peterz@infradead.org" <peterz@infradead.org>,
"torvalds@linux-foundation.org" <torvalds@linux-foundation.org>,
"ak@linux.intel.com" <ak@linux.intel.com>,
"riel@redhat.com" <riel@redhat.com>,
"keescook@google.com" <keescook@google.com>,
"gnomes@lxorguk.ukuu.org.uk" <gnomes@lxorguk.ukuu.org.uk>,
"pjt@google.com" <pjt@google.com>,
"dave.hansen@intel.com" <dave.hansen@intel.com>,
"luto@amacapital.net" <luto@amacapital.net>,
"jikos@kernel.org" <jikos@kernel.org>,
"gregkh@linux-foundation.org" <gregkh@linux-foundation.org>
Subject: Re: [PATCH v3 01/13] x86/retpoline: Add initial retpoline support
Date: Mon, 08 Jan 2018 21:50:50 +0000 [thread overview]
Message-ID: <1515448250.4423.33.camel@infradead.org> (raw)
In-Reply-To: <20180107140351.iukmbuf2xkqtvyoz@pd.tnic>
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On Sun, 2018-01-07 at 15:03 +0100, Borislav Petkov wrote:
>
> My fear is if some funky compiler changes the sizes of the insns in
> RETPOLINE_CALL/JMP and then the padding becomes wrong. But looking at the
> labels, they're all close so you have a 2-byte jmp already and the
>
> call 1112f
>
> should be ok. The MOV is reg,(reg) which should not change size of 4...
>
> But I'm remaining cautious here.
Right. I forget the specifics, but I've *watched* LLVM break carefully
hand-crafted asm code by emitting 4-byte variants when we expected 2-
byte, etc.
On the whole, I'm sufficiently unhappy with making such assumptions,
that I think the cure is worse than the disease. We can live with that
*one* out-of-line call to the thunk in the syscall case, and that was
the *only* one that really needed the call to be at the end.
Note that in the alternative case there, we don't even need to load it
into a register at all. We could do our own alternatives specially for
that case, and hand-tune the lengths only for them. But *with* a sanity
check to break the build on mismatch.
I don't think it's worth it at this point though.
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next prev parent reply other threads:[~2018-01-08 21:50 UTC|newest]
Thread overview: 79+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-01-04 9:10 [RFC] Retpoline: Binary mitigation for branch-target-injection (aka "Spectre") Paul Turner
2018-01-04 9:12 ` Paul Turner
2018-01-04 9:24 ` Paul Turner
2018-01-04 9:48 ` Greg Kroah-Hartman
2018-01-04 9:56 ` Woodhouse, David
2018-01-04 9:30 ` Woodhouse, David
2018-01-04 14:36 ` [PATCH v3 01/13] x86/retpoline: Add initial retpoline support David Woodhouse
2018-01-04 18:03 ` Linus Torvalds
2018-01-04 19:32 ` Woodhouse, David
2018-01-04 18:17 ` Alexei Starovoitov
2018-01-04 18:25 ` Linus Torvalds
2018-01-04 18:36 ` Alexei Starovoitov
2018-01-04 19:27 ` David Woodhouse
2018-01-05 10:28 ` Paul Turner
2018-01-05 10:55 ` David Woodhouse
2018-01-05 11:19 ` Paul Turner
2018-01-05 11:25 ` Paul Turner
2018-01-05 11:26 ` Paolo Bonzini
2018-01-05 12:20 ` Paul Turner
2018-01-05 10:40 ` Paul Turner
2018-01-04 18:40 ` Andi Kleen
2018-01-05 10:32 ` Paul Turner
2018-01-05 12:54 ` Thomas Gleixner
2018-01-05 13:01 ` Juergen Gross
2018-01-05 13:03 ` Thomas Gleixner
2018-01-05 13:56 ` Woodhouse, David
2018-01-05 16:41 ` Woodhouse, David
2018-01-05 16:45 ` Borislav Petkov
2018-01-05 17:08 ` Josh Poimboeuf
2018-01-06 0:30 ` Borislav Petkov
2018-01-06 8:23 ` David Woodhouse
2018-01-06 17:02 ` Borislav Petkov
2018-01-07 9:40 ` David Woodhouse
2018-01-07 11:46 ` Borislav Petkov
2018-01-07 12:21 ` David Woodhouse
2018-01-07 14:03 ` Borislav Petkov
2018-01-08 21:50 ` David Woodhouse [this message]
2018-01-08 5:06 ` Josh Poimboeuf
2018-01-08 7:55 ` Woodhouse, David
2018-01-05 17:12 ` Woodhouse, David
2018-01-05 17:28 ` Linus Torvalds
2018-01-05 17:48 ` David Woodhouse
2018-01-05 18:05 ` Andi Kleen
2018-01-05 20:32 ` Woodhouse, David
2018-01-05 21:11 ` Brian Gerst
2018-01-05 22:16 ` Woodhouse, David
2018-01-05 22:43 ` Borislav Petkov
2018-01-05 22:00 ` Woodhouse, David
2018-01-05 22:06 ` Borislav Petkov
2018-01-05 23:50 ` Linus Torvalds
2018-01-06 10:53 ` Woodhouse, David
2018-01-04 14:36 ` [PATCH v3 02/13] x86/retpoline/crypto: Convert crypto assembler indirect jumps David Woodhouse
2018-01-04 14:37 ` [PATCH v3 03/13] x86/retpoline/entry: Convert entry " David Woodhouse
2018-01-04 14:46 ` Dave Hansen
2018-01-04 14:49 ` Woodhouse, David
2018-01-04 14:37 ` [PATCH v3 04/13] x86/retpoline/ftrace: Convert ftrace " David Woodhouse
2018-01-04 14:37 ` [PATCH v3 05/13] x86/retpoline/hyperv: Convert " David Woodhouse
2018-01-04 14:37 ` [PATCH v3 06/13] x86/retpoline/xen: Convert Xen hypercall " David Woodhouse
2018-01-04 15:10 ` Juergen Gross
2018-01-04 15:18 ` David Woodhouse
2018-01-04 15:54 ` Juergen Gross
2018-01-04 14:37 ` [PATCH v3 07/13] x86/retpoline/checksum32: Convert assembler " David Woodhouse
2018-01-04 14:37 ` [PATCH v3 08/13] x86/alternatives: Add missing \n at end of ALTERNATIVE inline asm David Woodhouse
2018-01-05 13:04 ` [tip:x86/pti] x86/alternatives: Add missing '\n' " tip-bot for David Woodhouse
2018-01-04 14:37 ` [PATCH v3 09/13] x86/retpoline/irq32: Convert assembler indirect jumps David Woodhouse
2018-01-04 14:37 ` [PATCH v3 10/13] x86/retpoline/pvops: " David Woodhouse
2018-01-04 15:02 ` Juergen Gross
2018-01-04 15:12 ` Woodhouse, David
2018-01-04 15:18 ` Andrew Cooper
2018-01-04 16:04 ` Juergen Gross
2018-01-04 16:37 ` Andi Kleen
2018-01-04 14:37 ` [PATCH v3 11/13] retpoline/taint: Taint kernel for missing retpoline in compiler David Woodhouse
2018-01-04 22:06 ` Justin Forbes
2018-01-04 14:37 ` [PATCH v3 12/13] retpoline/objtool: Disable some objtool warnings David Woodhouse
2018-01-04 14:37 ` [PATCH v3 13/13] retpoline: Attempt to quiten objtool warning for unreachable code David Woodhouse
2018-01-04 16:18 ` [RFC] Retpoline: Binary mitigation for branch-target-injection (aka "Spectre") Andy Lutomirski
2018-01-04 16:24 ` David Woodhouse
2018-01-05 10:49 ` Paul Turner
2018-01-05 11:43 ` Woodhouse, David
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