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>

1 files changed, 7 insertions, 5 deletions

diff --git a/arch/i386/xen/enlighten.c b/arch/i386/xen/enlighten.c
index 9a8c118..f0c3751 100644
--- a/arch/i386/xen/enlighten.c
+++ b/arch/i386/xen/enlighten.c
@@ -842,7 +842,8 @@ void __init xen_setup_vcpu_info_placement(void)
 	}
 }
 
-static unsigned xen_patch(u8 type, u16 clobbers, void *insns, unsigned len)
+static unsigned xen_patch(u8 type, u16 clobbers, void *insnbuf,
+			  unsigned long addr, unsigned len)
 {
 	char *start, *end, *reloc;
 	unsigned ret;
@@ -869,7 +870,7 @@ static unsigned xen_patch(u8 type, u16 clobbers, void *insns, unsigned len)
 		if (start == NULL || (end-start) > len)
 			goto default_patch;
 
-		ret = paravirt_patch_insns(insns, len, start, end);
+		ret = paravirt_patch_insns(insnbuf, len, start, end);
 
 		/* Note: because reloc is assigned from something that
 		   appears to be an array, gcc assumes it's non-null,
@@ -877,8 +878,8 @@ static unsigned xen_patch(u8 type, u16 clobbers, void *insns, unsigned len)
 		   end. */
 		if (reloc > start && reloc < end) {
 			int reloc_off = reloc - start;
-			long *relocp = (long *)(insns + reloc_off);
-			long delta = start - (char *)insns;
+			long *relocp = (long *)(insnbuf + reloc_off);
+			long delta = start - (char *)addr;
 
 			*relocp += delta;
 		}
@@ -886,7 +887,8 @@ static unsigned xen_patch(u8 type, u16 clobbers, void *insns, unsigned len)
 
 	default_patch:
 	default:
-		ret = paravirt_patch_default(type, clobbers, insns, len);
+		ret = paravirt_patch_default(type, clobbers, insnbuf,
+					     addr, len);
 		break;
 	}