i386: Make patching more robust, fix paravirt issue
Commit 19d36ccdc34f5ed444f8a6af0cbfdb6790eb1177 "x86: Fix alternatives
and kprobes to remap write-protected kernel text" uses code which is
being patched for patching.
In particular, paravirt_ops does patching in two stages: first it
calls paravirt_ops.patch, then it fills any remaining instructions
with nop_out(). nop_out calls text_poke() which calls
lookup_address() which calls pgd_val() (aka paravirt_ops.pgd_val):
that call site is one of the places we patch.
If we always do patching as one single call to text_poke(), we only
need make sure we're not patching the memcpy in text_poke itself.
This means the prototype to paravirt_ops.patch needs to change, to
marshal the new code into a buffer rather than patching in place as it
does now. It also means all patching goes through text_poke(), which
is known to be safe (apply_alternatives is also changed to make a
single patch).
AK: fix compilation on x86-64 (bad rusty!)
AK: fix boot on x86-64 (sigh)
AK: merged with other patches
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/arch/i386/kernel/alternative.c b/arch/i386/kernel/alternative.c
index c85598a..27a6b0c 100644
--- a/arch/i386/kernel/alternative.c
+++ b/arch/i386/kernel/alternative.c
@@ -11,6 +11,8 @@
#include <asm/mce.h>
#include <asm/nmi.h>
+#define MAX_PATCH_LEN (255-1)
+
#ifdef CONFIG_HOTPLUG_CPU
static int smp_alt_once;
@@ -148,7 +150,8 @@
#endif /* CONFIG_X86_64 */
-static void nop_out(void *insns, unsigned int len)
+/* Use this to add nops to a buffer, then text_poke the whole buffer. */
+static void add_nops(void *insns, unsigned int len)
{
unsigned char **noptable = find_nop_table();
@@ -156,7 +159,7 @@
unsigned int noplen = len;
if (noplen > ASM_NOP_MAX)
noplen = ASM_NOP_MAX;
- text_poke(insns, noptable[noplen], noplen);
+ memcpy(insns, noptable[noplen], noplen);
insns += noplen;
len -= noplen;
}
@@ -174,15 +177,15 @@
void apply_alternatives(struct alt_instr *start, struct alt_instr *end)
{
struct alt_instr *a;
- u8 *instr;
- int diff;
+ char insnbuf[MAX_PATCH_LEN];
DPRINTK("%s: alt table %p -> %p\n", __FUNCTION__, start, end);
for (a = start; a < end; a++) {
+ u8 *instr = a->instr;
BUG_ON(a->replacementlen > a->instrlen);
+ BUG_ON(a->instrlen > sizeof(insnbuf));
if (!boot_cpu_has(a->cpuid))
continue;
- instr = a->instr;
#ifdef CONFIG_X86_64
/* vsyscall code is not mapped yet. resolve it manually. */
if (instr >= (u8 *)VSYSCALL_START && instr < (u8*)VSYSCALL_END) {
@@ -191,9 +194,10 @@
__FUNCTION__, a->instr, instr);
}
#endif
- memcpy(instr, a->replacement, a->replacementlen);
- diff = a->instrlen - a->replacementlen;
- nop_out(instr + a->replacementlen, diff);
+ memcpy(insnbuf, a->replacement, a->replacementlen);
+ add_nops(insnbuf + a->replacementlen,
+ a->instrlen - a->replacementlen);
+ text_poke(instr, insnbuf, a->instrlen);
}
}
@@ -215,16 +219,18 @@
static void alternatives_smp_unlock(u8 **start, u8 **end, u8 *text, u8 *text_end)
{
u8 **ptr;
+ char insn[1];
if (noreplace_smp)
return;
+ add_nops(insn, 1);
for (ptr = start; ptr < end; ptr++) {
if (*ptr < text)
continue;
if (*ptr > text_end)
continue;
- nop_out(*ptr, 1);
+ text_poke(*ptr, insn, 1);
};
}
@@ -351,6 +357,7 @@
struct paravirt_patch_site *end)
{
struct paravirt_patch_site *p;
+ char insnbuf[MAX_PATCH_LEN];
if (noreplace_paravirt)
return;
@@ -358,13 +365,15 @@
for (p = start; p < end; p++) {
unsigned int used;
- used = paravirt_ops.patch(p->instrtype, p->clobbers, p->instr,
- p->len);
+ BUG_ON(p->len > MAX_PATCH_LEN);
+ used = paravirt_ops.patch(p->instrtype, p->clobbers, insnbuf,
+ (unsigned long)p->instr, p->len);
BUG_ON(used > p->len);
/* Pad the rest with nops */
- nop_out(p->instr + used, p->len - used);
+ add_nops(insnbuf + used, p->len - used);
+ text_poke(p->instr, insnbuf, p->len);
}
}
extern struct paravirt_patch_site __start_parainstructions[],