x86: Fix alternatives and kprobes to remap write-protected kernel text

Reenable kprobes and alternative patching when the kernel text is write
protected by DEBUG_RODATA

Add a general utility function to change write protected text.  The new
function remaps the code using vmap to write it and takes care of CPU
synchronization.  It also does CLFLUSH to make icache recovery faster.

There are some limitations on when the function can be used, see the
comment.

This is a newer version that also changes the paravirt_ops code.
text_poke also supports multi byte patching now.

Contains bug fixes from Zach Amsden and suggestions from Mathieu
Desnoyers.

Cc: Jan Beulich <jbeulich@novell.com>
Cc: Jeremy Fitzhardinge <jeremy@goop.org>
Cc: Mathieu Desnoyers <compudj@krystal.dyndns.org>
Cc: Zach Amsden <zach@vmware.com>
Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 13 insertions, 4 deletions

diff --git a/arch/i386/kernel/paravirt.c b/arch/i386/kernel/paravirt.c
index 53f07a8275e3..79c167fcaee9 100644
--- a/arch/i386/kernel/paravirt.c
+++ b/arch/i386/kernel/paravirt.c
@@ -124,20 +124,28 @@ unsigned paravirt_patch_ignore(unsigned len)
         return len;
 }
 
+struct branch {
+        unsigned char opcode;
+        u32 delta;
+} __attribute__((packed));
+
 unsigned paravirt_patch_call(void *target, u16 tgt_clobbers,
                              void *site, u16 site_clobbers,
                              unsigned len)
 {
         unsigned char *call = site;
         unsigned long delta = (unsigned long)target - (unsigned long)(call+5);
+        struct branch b;
 
         if (tgt_clobbers & ~site_clobbers)
                 return len;     /* target would clobber too much for this site */
         if (len < 5)
                 return len;     /* call too long for patch site */
 
-        *call++ = 0xe8;         /* call */
-        *(unsigned long *)call = delta;
+        b.opcode = 0xe8; /* call */
+        b.delta = delta;
+        BUILD_BUG_ON(sizeof(b) != 5);
+        text_poke(call, (unsigned char *)&b, 5);
 
         return 5;
 }
@@ -150,8 +158,9 @@ unsigned paravirt_patch_jmp(void *target, void *site, unsigned len)
         if (len < 5)
                 return len;     /* call too long for patch site */
 
-        *jmp++ = 0xe9;          /* jmp */
-        *(unsigned long *)jmp = delta;
+        b.opcode = 0xe9;        /* jmp */
+        b.delta = delta;
+        text_poke(call, (unsigned char *)&b, 5);
 
         return 5;
 }