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, 21 insertions, 14 deletions

diff --git a/arch/i386/kernel/vmi.c b/arch/i386/kernel/vmi.c
index 72042bb7ec9..18673e0f193 100644
--- a/arch/i386/kernel/vmi.c
+++ b/arch/i386/kernel/vmi.c
@@ -87,12 +87,14 @@ struct vmi_timer_ops vmi_timer_ops;
 #define IRQ_PATCH_INT_MASK 0
 #define IRQ_PATCH_DISABLE  5
 
-static inline void patch_offset(unsigned char *eip, unsigned char *dest)
+static inline void patch_offset(void *insnbuf,
+                                unsigned long eip, unsigned long dest)
 {
-        *(unsigned long *)(eip+1) = dest-eip-5;
+        *(unsigned long *)(insnbuf+1) = dest-eip-5;
 }
 
-static unsigned patch_internal(int call, unsigned len, void *insns)
+static unsigned patch_internal(int call, unsigned len, void *insnbuf,
+                               unsigned long eip)
 {
         u64 reloc;
         struct vmi_relocation_info *const rel = (struct vmi_relocation_info *)&reloc;
@@ -100,14 +102,14 @@ static unsigned patch_internal(int call, unsigned len, void *insns)
         switch(rel->type) {
                 case VMI_RELOCATION_CALL_REL:
                         BUG_ON(len < 5);
-                        *(char *)insns = MNEM_CALL;
-                        patch_offset(insns, rel->eip);
+                        *(char *)insnbuf = MNEM_CALL;
+                        patch_offset(insnbuf, eip, (unsigned long)rel->eip);
                         return 5;
 
                 case VMI_RELOCATION_JUMP_REL:
                         BUG_ON(len < 5);
-                        *(char *)insns = MNEM_JMP;
-                        patch_offset(insns, rel->eip);
+                        *(char *)insnbuf = MNEM_JMP;
+                        patch_offset(insnbuf, eip, (unsigned long)rel->eip);
                         return 5;
 
                 case VMI_RELOCATION_NOP:
@@ -128,21 +130,26 @@ static unsigned patch_internal(int call, unsigned len, void *insns)
  * Apply patch if appropriate, return length of new instruction
  * sequence.  The callee does nop padding for us.
  */
-static unsigned vmi_patch(u8 type, u16 clobbers, void *insns, unsigned len)
+static unsigned vmi_patch(u8 type, u16 clobbers, void *insns,
+                          unsigned long eip, unsigned len)
 {
         switch (type) {
                 case PARAVIRT_PATCH(irq_disable):
-                        return patch_internal(VMI_CALL_DisableInterrupts, len, insns);
+                        return patch_internal(VMI_CALL_DisableInterrupts, len,
+                                              insns, eip);
                 case PARAVIRT_PATCH(irq_enable):
-                        return patch_internal(VMI_CALL_EnableInterrupts, len, insns);
+                        return patch_internal(VMI_CALL_EnableInterrupts, len,
+                                              insns, eip);
                 case PARAVIRT_PATCH(restore_fl):
-                        return patch_internal(VMI_CALL_SetInterruptMask, len, insns);
+                        return patch_internal(VMI_CALL_SetInterruptMask, len,
+                                              insns, eip);
                 case PARAVIRT_PATCH(save_fl):
-                        return patch_internal(VMI_CALL_GetInterruptMask, len, insns);
+                        return patch_internal(VMI_CALL_GetInterruptMask, len,
+                                              insns, eip);
                 case PARAVIRT_PATCH(iret):
-                        return patch_internal(VMI_CALL_IRET, len, insns);
+                        return patch_internal(VMI_CALL_IRET, len, insns, eip);
                 case PARAVIRT_PATCH(irq_enable_sysexit):
-                        return patch_internal(VMI_CALL_SYSEXIT, len, insns);
+                        return patch_internal(VMI_CALL_SYSEXIT, len, insns, eip);
                 default:
                         break;
         }