Commit-ID: 4fd4b6e5537cec5b56db0b22546dd439ebb26830
Gitweb: http://git.kernel.org/tip/4fd4b6e5537cec5b56db0b22546dd439ebb26830
Author: Borislav Petkov <bp@xxxxxxx>
AuthorDate: Sat, 10 Jan 2015 20:34:07 +0100
Committer: Borislav Petkov <bp@xxxxxxx>
CommitDate: Mon, 23 Feb 2015 13:44:12 +0100
x86/alternatives: Use optimized NOPs for padding
Alternatives allow now for an 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 by
adding alt_instr.padlen-sized NOPs at the old instruction address.
Cc: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
Signed-off-by: Borislav Petkov <bp@xxxxxxx>
---
arch/x86/kernel/alternative.c | 14 +++++++++++++-
1 file changed, 13 insertions(+), 1 deletion(-)
diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index 715af37..af397cc 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -323,6 +323,14 @@ done:
n_dspl, (unsigned long)orig_insn + n_dspl + repl_len);
}
+static void __init_or_module optimize_nops(struct alt_instr *a, u8 *instr)
+{
+ add_nops(instr + (a->instrlen - a->padlen), a->padlen);
+
+ DUMP_BYTES(instr, a->instrlen, "%p: [%d:%d) optimized NOPs: ",
+ instr, a->instrlen - a->padlen, a->padlen);
+}
+
/*
* 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 +362,12 @@ 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 (a->padlen > 1)
+ optimize_nops(a, instr);
+
continue;
+ }
DPRINTK("feat: %d*32+%d, old: (%p, len: %d), repl: (%p, len: %d)",
a->cpuid >> 5,
--
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