From: Borislav Petkov <bp@alien8.de>
To: Quentin Casasnovas <quentin.casasnovas@oracle.com>
Cc: X86 ML <x86@kernel.org>, LKML <linux-kernel@vger.kernel.org>,
"H. Peter Anvin" <hpa@zytor.com>, Ingo Molnar <mingo@kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
Oleg Nesterov <oleg@redhat.com>,
Andy Lutomirski <luto@amacapital.net>
Subject: Re: [PATCH] x86/xsave: Robustify and merge macros
Date: Sat, 4 Apr 2015 12:29:22 +0200 [thread overview]
Message-ID: <20150404102922.GC21152@pd.tnic> (raw)
In-Reply-To: <20150404101155.GB5922@chrystal.uk.oracle.com>
On Sat, Apr 04, 2015 at 12:11:55PM +0200, Quentin Casasnovas wrote:
> So I'm not claiming I've spent the time to fully understand this macro but
> it looks like it's doing the right thing on my dummy tests:
>
> http://pastebin.com/DDhtZQgX
Cool, I'll play with it a bit when I get back.
> Did you also change it in the alternative.h file BTW?
Yeah, see below.
> Good catch for the missing parenthesis!
:-)
> So I _think_ it's OK but it would be re-assuring if somebody else could
> have a look as well just in case.. :)
Yeah, once I test it on everything here, I'll send it out for people to
poke holes too. Current version below.
> Do you have a cleaned up version of the patch you're planning to apply on
> top of tip/master instead of just snippets?
See below.
> This way we can hammer it with
> different calls to ALTERNATIVE_2 and alternative_2 to check it's good?
> I'll have to leave soonish though..
Thanks a lot for this, much appreciated!
---
From: Borislav Petkov <bp@suse.de>
Date: Sat, 4 Apr 2015 10:02:42 +0200
Subject: [PATCH] ALTERNATIVE_2 tentative fix
Signed-off-by: Borislav Petkov <bp@suse.de>
Reported-by: Quentin Casasnovas <quentin.casasnovas@oracle.com>
---
arch/x86/include/asm/alternative-asm.h | 14 ++++++++++++--
arch/x86/include/asm/alternative.h | 14 ++++++++++----
arch/x86/kernel/alternative.c | 4 ++--
3 files changed, 24 insertions(+), 8 deletions(-)
diff --git a/arch/x86/include/asm/alternative-asm.h b/arch/x86/include/asm/alternative-asm.h
index 524bddce0b76..bdf02eeee765 100644
--- a/arch/x86/include/asm/alternative-asm.h
+++ b/arch/x86/include/asm/alternative-asm.h
@@ -45,12 +45,22 @@
.popsection
.endm
+#define old_len 141b-140b
+#define new_len1 144f-143f
+#define new_len2 145f-144f
+
+/*
+ * max without conditionals. Idea adapted from:
+ * http://graphics.stanford.edu/~seander/bithacks.html#IntegerMinOrMax
+ */
+#define alt_max_short(a, b) ((a) ^ (((a) ^ (b)) & -(-((a) < (b)))))
+
.macro ALTERNATIVE_2 oldinstr, newinstr1, feature1, newinstr2, feature2
140:
\oldinstr
141:
- .skip -(((144f-143f)-(141b-140b)) > 0) * ((144f-143f)-(141b-140b)),0x90
- .skip -(((145f-144f)-(144f-143f)-(141b-140b)) > 0) * ((145f-144f)-(144f-143f)-(141b-140b)),0x90
+ .skip -((alt_max_short(new_len1, new_len2) - (old_len)) > 0) * \
+ (alt_max_short(new_len1, new_len2) - (old_len)),0x90
142:
.pushsection .altinstructions,"a"
diff --git a/arch/x86/include/asm/alternative.h b/arch/x86/include/asm/alternative.h
index 5aef6a97d80e..a542c8017a89 100644
--- a/arch/x86/include/asm/alternative.h
+++ b/arch/x86/include/asm/alternative.h
@@ -96,13 +96,19 @@ static inline int alternatives_text_reserved(void *start, void *end)
alt_end_marker ":\n"
/*
+ * max without conditionals. Idea adapted from:
+ * http://graphics.stanford.edu/~seander/bithacks.html#IntegerMinOrMax
+ */
+#define alt_max_short(a, b) "((" a ") ^ (((" a ") ^ (" b ")) & -(-((" a ") - (" b ")))))"
+
+/*
* Pad the second replacement alternative with additional NOPs if it is
* additionally longer than the first replacement alternative.
*/
-#define OLDINSTR_2(oldinstr, num1, num2) \
- __OLDINSTR(oldinstr, num1) \
- ".skip -(((" alt_rlen(num2) ")-(" alt_rlen(num1) ")-(662b-661b)) > 0) * " \
- "((" alt_rlen(num2) ")-(" alt_rlen(num1) ")-(662b-661b)),0x90\n" \
+#define OLDINSTR_2(oldinstr, num1, num2) \
+ "661:\n\t" oldinstr "\n662:\n" \
+ ".skip -((" alt_max_short(alt_rlen(num1), alt_rlen(num2)) " - (" alt_slen ")) > 0) * " \
+ "(" alt_max_short(alt_rlen(num1), alt_rlen(num2)) " - (" alt_slen ")), 0x90\n" \
alt_end_marker ":\n"
#define ALTINSTR_ENTRY(feature, num) \
diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index 5c993c94255e..7c4ad005d7a0 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -369,11 +369,11 @@ void __init_or_module apply_alternatives(struct alt_instr *start,
continue;
}
- DPRINTK("feat: %d*32+%d, old: (%p, len: %d), repl: (%p, len: %d)",
+ DPRINTK("feat: %d*32+%d, old: (%p, len: %d), repl: (%p, len: %d), pad: %d",
a->cpuid >> 5,
a->cpuid & 0x1f,
instr, a->instrlen,
- replacement, a->replacementlen);
+ replacement, a->replacementlen, a->padlen);
DUMP_BYTES(instr, a->instrlen, "%p: old_insn: ", instr);
DUMP_BYTES(replacement, a->replacementlen, "%p: rpl_insn: ", replacement);
--
2.3.3
--
Regards/Gruss,
Boris.
ECO tip #101: Trim your mails when you reply.
--
next prev parent reply other threads:[~2015-04-04 10:31 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-04-02 13:11 [PATCH] x86/xsave: Robustify and merge macros Borislav Petkov
2015-04-02 15:52 ` Quentin Casasnovas
2015-04-02 16:12 ` Borislav Petkov
2015-04-02 16:33 ` Quentin Casasnovas
2015-04-02 16:45 ` Borislav Petkov
2015-04-03 14:06 ` Quentin Casasnovas
2015-04-03 14:14 ` Quentin Casasnovas
2015-04-03 15:23 ` Borislav Petkov
2015-04-03 15:40 ` Quentin Casasnovas
2015-04-03 17:06 ` Borislav Petkov
2015-04-03 17:33 ` Quentin Casasnovas
2015-04-03 17:48 ` Borislav Petkov
2015-04-03 20:42 ` Quentin Casasnovas
2015-04-04 7:34 ` Borislav Petkov
2015-04-04 8:36 ` Quentin Casasnovas
2015-04-04 9:25 ` Borislav Petkov
2015-04-04 10:11 ` Quentin Casasnovas
2015-04-04 10:29 ` Borislav Petkov [this message]
2015-04-04 13:32 ` Borislav Petkov
2015-04-04 13:34 ` [PATCH] x86/alternatives: Fix ALTERNATIVE_2 padding generation properly Borislav Petkov
2015-04-07 9:27 ` Quentin Casasnovas
2015-04-07 9:40 ` [tip:x86/asm] " tip-bot for Borislav Petkov
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