linux-kernel - [PATCH v1 05/12] x86, alternatives: Use optimized NOPs for padding

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <1422987390-17878-6-git-send-email-bp@alien8.de>
Date:	Tue,  3 Feb 2015 19:16:23 +0100
From:	Borislav Petkov <bp@...en8.de>
To:	X86 ML <x86@...nel.org>
Cc:	LKML <linux-kernel@...r.kernel.org>
Subject: [PATCH v1 05/12] x86, alternatives: Use optimized NOPs for padding

From: Borislav Petkov <bp@...e.de>

Alternatives allow now for empty old instruction. In this case we go
and pad the space with NOPs at assembly time. However, there are the
optimal, longer NOPs which should be used. Do that at patching time.

Signed-off-by: Borislav Petkov <bp@...e.de>
---
 arch/x86/kernel/alternative.c | 20 +++++++++++++++++++-
 1 file changed, 19 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index 715af37bf008..dd0cdb6b179c 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -323,6 +323,21 @@ done:
 		n_dspl, (unsigned long)orig_insn + n_dspl + repl_len);
 }
 
+static void __init_or_module optimize_nops(u8 *instr, u8 max_len)
+{
+	int i = 0;
+
+	while (instr[i] == 0x90 && i < max_len)
+		i++;
+
+	if (!i)
+		return;
+
+	add_nops(instr, i);
+
+	DUMP_BYTES(instr, i, "%p: optimized NOPs: ", instr);
+}
+
 /*
  * Replace instructions with better alternatives for this CPU type. This runs
  * before SMP is initialized to avoid SMP problems with self modifying code.
@@ -354,8 +369,11 @@ void __init_or_module apply_alternatives(struct alt_instr *start,
 		replacement = (u8 *)&a->repl_offset + a->repl_offset;
 		BUG_ON(a->instrlen > sizeof(insnbuf));
 		BUG_ON(a->cpuid >= (NCAPINTS + NBUGINTS) * 32);
-		if (!boot_cpu_has(a->cpuid))
+		if (!boot_cpu_has(a->cpuid)) {
+			if (instr[0] == 0x90)
+				optimize_nops(instr, a->instrlen);
 			continue;
+		}
 
 		DPRINTK("feat: %d*32+%d, old: (%p, len: %d), repl: (%p, len: %d)",
 			a->cpuid >> 5,
-- 
2.2.0.33.gc18b867

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/