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Subject[PATCH 3/5 v2] x86/jump-label: Add safety checks to jump label conversions
From: Steven Rostedt <srostedt@redhat.com>

As with all modifying of kernel text, we need to be very paranoid.

When converting the jump label locations to and from nops to jumps
a check has been added to make sure what we are replacing is what we
expect, otherwise we bug.

Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Jason Baron <jbaron@redhat.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
arch/x86/kernel/jump_label.c | 32 ++++++++++++++++++++++++++++----
1 files changed, 28 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kernel/jump_label.c b/arch/x86/kernel/jump_label.c
index cd42721..12a8812 100644
--- a/arch/x86/kernel/jump_label.c
+++ b/arch/x86/kernel/jump_label.c
@@ -26,16 +26,40 @@ union jump_code_union {

static void __jump_label_transform(struct jump_entry *entry,
enum jump_label_type type,
- void *(*poker)(void *, const void *, size_t))
+ void *(*poker)(void *, const void *, size_t),
+ int init)
{
union jump_code_union code;
+ const unsigned char *ideal_nop = ideal_nops[NOP_ATOMIC5];

if (type == JUMP_LABEL_ENABLE) {
+ /*
+ * We are enabling this jump label. If it is not a nop
+ * then something must have gone wrong.
+ */
+ BUG_ON(memcmp((void *)entry->code, ideal_nop, 5) != 0);
+
code.jump = 0xe9;
code.offset = entry->target -
(entry->code + JUMP_LABEL_NOP_SIZE);
- } else
+ } else {
+ /*
+ * We are disabling this jump label. If it is not what
+ * we think it is, then something must have gone wrong.
+ * If this is the first initialization call, then we
+ * are converting the default nop to the ideal nop.
+ */
+ if (init) {
+ const unsigned char default_nop[] = { JUMP_LABEL_INIT_NOP };
+ BUG_ON(memcmp((void *)entry->code, default_nop, 5) != 0);
+ } else {
+ code.jump = 0xe9;
+ code.offset = entry->target -
+ (entry->code + JUMP_LABEL_NOP_SIZE);
+ BUG_ON(memcmp((void *)entry->code, &code, 5) != 0);
+ }
memcpy(&code, ideal_nops[NOP_ATOMIC5], JUMP_LABEL_NOP_SIZE);
+ }

(*poker)((void *)entry->code, &code, JUMP_LABEL_NOP_SIZE);
}
@@ -45,7 +69,7 @@ void arch_jump_label_transform(struct jump_entry *entry,
{
get_online_cpus();
mutex_lock(&text_mutex);
- __jump_label_transform(entry, type, text_poke_smp);
+ __jump_label_transform(entry, type, text_poke_smp, 0);
mutex_unlock(&text_mutex);
put_online_cpus();
}
@@ -71,7 +95,7 @@ void arch_jump_label_transform_static(struct jump_entry *entry,
update = 1;
}
if (update)
- __jump_label_transform(entry, type, text_poke_early);
+ __jump_label_transform(entry, type, text_poke_early, 1);
}

#endif
--
1.7.8.3

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