From: Masami Hiramatsu <mhiramat@kernel.org>
Date: Wed, 27 Nov 2019 14:56:52 +0900
Subject: x86/alternatives: Sync bp_patching update for avoiding NULL pointer
exception
Git-commit: 285a54efe3861976af9d15e85ff8c91a78d1407b
Patch-mainline: v5.6-rc1
References: bsc#1152489
ftracetest multiple_kprobes.tc testcase hits the following NULL pointer
exception:
BUG: kernel NULL pointer dereference, address: 0000000000000000
PGD 800000007bf60067 P4D 800000007bf60067 PUD 7bf5f067 PMD 0
Oops: 0000 [#1] PREEMPT SMP PTI
RIP: 0010:poke_int3_handler+0x39/0x100
Call Trace:
<IRQ>
do_int3+0xd/0xf0
int3+0x42/0x50
RIP: 0010:sched_clock+0x6/0x10
poke_int3_handler+0x39 was alternatives:958:
static inline void *text_poke_addr(struct text_poke_loc *tp)
{
return _stext + tp->rel_addr; <------ Here is line #958
}
This seems to be caused by tp (bp_patching.vec) being NULL but
bp_patching.nr_entries != 0. There is a small chance for this
to happen, because we have no synchronization between the zeroing
of bp_patching.nr_entries and before clearing bp_patching.vec.
Steve suggested we could fix this by adding sync_core(), because int3
is done with interrupts disabled, and the on_each_cpu() requires
all CPUs to have had their interrupts enabled.
[ mingo: Edited the comments and the changelog. ]
Suggested-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Tested-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: bristot@redhat.com
Fixes: c0213b0ac03c ("x86/alternative: Batch of patch operations")
Link: https://lkml.kernel.org/r/157483421229.25881.15314414408559963162.stgit@devnote2
Signed-off-by: Ingo Molnar <mingo@kernel.org>
[ bp: Use text_poke_sync()'s function body because it is not there yet. ]
Acked-by: Borislav Petkov <bp@suse.de>
---
arch/x86/kernel/alternative.c | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -1109,8 +1109,14 @@ void text_poke_bp_batch(struct text_poke
* sync_core() implies an smp_mb() and orders this store against
* the writing of the new instruction.
*/
- bp_patching.vec = NULL;
bp_patching.nr_entries = 0;
+ /*
+ * This sync_core () call ensures that all INT3 handlers in progress
+ * have finished. This allows poke_int3_handler() after this to
+ * avoid touching bp_paching.vec by checking nr_entries == 0.
+ */
+ on_each_cpu(do_sync_core, NULL, 1);
+ bp_patching.vec = NULL;
}
void text_poke_loc_init(struct text_poke_loc *tp, void *addr,