From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Google-Smtp-Source: AH8x226Rsin15U22+C3MVmaa9iIIVcKy6WEvTteN3SSgWqIu/4P4JVoLoR+wMF84R+cDXjbnowGc ARC-Seal: i=1; a=rsa-sha256; t=1517246021; cv=none; d=google.com; s=arc-20160816; b=cyF4bq7MshBxq3nbWiGvSlzKtzV0MpiB/+jckIkEBm4ALPzPEkfEH0OeYZKSld32UC BiDLkN6eO8dV6kUtw0+Ixd3hf/TPalDkAMDb9VRP8gHTB9nhwwuQGock6ZknhPBEV2++ J3AU5cJYATvZhN32rHzN9H1ZdYUyAXzv3ZN0aCY6mKr3N6y3hZ8W/uOo8t6MxZ4GmDxC vLvEepf2RbZaiM+nha2zLnP1+llqFjIVdLUbECm9yjbZKdZ67V5Oc9tWkn0O37KKnl23 va8Vgwi97CW9U7js9jubxbx1Oeg2CRbVYSfQQKiVpic3MRYF5sSKH627NSce/TAFi3OX Ew4A== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=user-agent:in-reply-to:content-transfer-encoding :content-disposition:mime-version:references:message-id:subject:cc :to:from:date:dkim-signature:arc-authentication-results; bh=ZHwnvf86blW3cl9Jg6W3ez8M/F0eA1bXNU7NJllH4Po=; b=ICiuSr0/IYaICB2dYLI+atzceNA4cvNpxYUz8JvDQFjffckv1lSTZaKrHQ2JE79tqZ AiAwHv7CG2QNqfF0rFNfwnRj2wA+5sBbQRstvl3bKkDAM7ATCNgGRqzNp5yOrLI0mlS7 yBfjfmauDPjzmLxXi89n2vQPXJ2sBbaGY46ho/KBvAsGnq33ZU3I2yrRn6HyJKY97p45 qfy2nMiBA6lz4EEe6RxlJdQEG5yxukFhjIuJVUkgb+3tZUE9l9Y6KuZc8eQHF+Kok5O/ FFwtsKMykIf51wbpCGbgwYVhlaukRDpDtL2P7p9LGmeK+LsZDICqWslfrYSDNt3Vtrr5 SF3w== ARC-Authentication-Results: i=1; mx.google.com; dkim=pass header.i=@infradead.org header.s=merlin.20170209 header.b=IKmZQL10; spf=pass (google.com: best guess record for domain of peterz@infradead.org designates 2001:8b0:10b:1231::1 as permitted sender) smtp.mailfrom=peterz@infradead.org Authentication-Results: mx.google.com; dkim=pass header.i=@infradead.org header.s=merlin.20170209 header.b=IKmZQL10; spf=pass (google.com: best guess record for domain of peterz@infradead.org designates 2001:8b0:10b:1231::1 as permitted sender) smtp.mailfrom=peterz@infradead.org Date: Mon, 29 Jan 2018 18:13:19 +0100 From: Peter Zijlstra To: Borislav Petkov Cc: David Woodhouse , X86 ML , LKML , Josh Poimboeuf , tim.c.chen@linux.intel.com, pjt@google.com, jikos@kernel.org, gregkh@linux-foundation.org, dave.hansen@intel.com, riel@redhat.com, luto@amacapital.net, torvalds@linux-foundation.org, ak@linux.intel.com, keescook@google.com Subject: Re: [PATCH v2 1/2] x86/retpoline: Simplify vmexit_fill_RSB() Message-ID: <20180129171319.GG2228@hirez.programming.kicks-ass.net> References: <20180126121139.31959-1-bp@alien8.de> <20180126121139.31959-4-bp@alien8.de> <1516970011.30244.223.camel@infradead.org> <20180126132431.fsbd3c3g2yreazy6@pd.tnic> <1516983879.30244.236.camel@infradead.org> <20180126164746.dpo7dswid5tjk2tz@pd.tnic> <20180126200616.5xfn244uzeu7ptyo@pd.tnic> <20180126200725.rueqb2m6b4w47eu3@pd.tnic> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20180126200725.rueqb2m6b4w47eu3@pd.tnic> User-Agent: Mutt/1.9.2 (2017-12-15) X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-THRID: =?utf-8?q?1590656989548468968?= X-GMAIL-MSGID: =?utf-8?q?1590947764117054706?= X-Mailing-List: linux-kernel@vger.kernel.org List-ID: On Fri, Jan 26, 2018 at 09:07:25PM +0100, Borislav Petkov wrote: > +.macro FILL_RETURN_BUFFER nr:req ftr:req > #ifdef CONFIG_RETPOLINE > + ALTERNATIVE "", "call __clear_rsb", \ftr > #endif > .endm > > @@ -206,15 +174,10 @@ extern char __indirect_thunk_end[]; > static inline void vmexit_fill_RSB(void) > { > #ifdef CONFIG_RETPOLINE > + alternative_input("", > + "call __fill_rsb", > + X86_FEATURE_RETPOLINE, > + ASM_NO_INPUT_CLOBBER("memory")); > #endif > } > > @@ -19,6 +20,37 @@ ENDPROC(__x86_indirect_thunk_\reg) > .endm > > /* > + * Google experimented with loop-unrolling and this turned out to be > + * the optimal version — two calls, each with their own speculation > + * trap should their return address end up getting used, in a loop. > + */ > +.macro BOINK_RSB nr:req sp:req > + push %_ASM_AX > + mov $(\nr / 2), %_ASM_AX > + .align 16 > +771: > + call 772f > +773: /* speculation trap */ > + pause > + lfence > + jmp 773b > + .align 16 > +772: > + call 774f > +775: /* speculation trap */ > + pause > + lfence > + jmp 775b > + .align 16 > +774: > + dec %_ASM_AX > + jnz 771b > + add $((BITS_PER_LONG/8) * \nr), \sp > + pop %_ASM_AX > +.endm > + > + > +/* > * Despite being an assembler file we can't just use .irp here > * because __KSYM_DEPS__ only uses the C preprocessor and would > * only see one instance of "__x86_indirect_thunk_\reg" rather > @@ -46,3 +78,15 @@ GENERATE_THUNK(r13) > GENERATE_THUNK(r14) > GENERATE_THUNK(r15) > #endif > + > +ENTRY(__fill_rsb) > + BOINK_RSB RSB_FILL_LOOPS, %_ASM_SP > + ret > +END(__fill_rsb) > +EXPORT_SYMBOL_GPL(__fill_rsb) > + > +ENTRY(__clear_rsb) > + BOINK_RSB RSB_CLEAR_LOOPS, %_ASM_SP > + ret > +END(__clear_rsb) > +EXPORT_SYMBOL_GPL(__clear_rsb) One thing I feel this ought to mention (in the Changelog probably) is that it looses one RET for SKL+. That is, where we used to have 16 'safe' RETs before this, we now have 15.