summaryrefslogtreecommitdiff
path: root/arch
diff options
context:
space:
mode:
authorBorislav Petkov <bp@suse.de>2015-01-10 20:34:07 +0100
committerBorislav Petkov <bp@suse.de>2015-02-23 13:44:12 +0100
commit4fd4b6e5537cec5b56db0b22546dd439ebb26830 (patch)
tree6a6ba144ac6e23d7fd71a70f4102cf46f7955f6c /arch
parent48c7a2509f9e237d8465399d9cdfe487d3212a23 (diff)
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@amacapital.net> Signed-off-by: Borislav Petkov <bp@suse.de>
Diffstat (limited to 'arch')
-rw-r--r--arch/x86/kernel/alternative.c14
1 files changed, 13 insertions, 1 deletions
diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index 715af37bf008..af397cc98d05 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,