[tip: x86/urgent] x86/alternatives: Sync core before enabling interrupts

[tip-bot2 for Thomas Gleixner]

The following commit has been merged into the x86/urgent branch of tip:

Commit-ID:     3ea1704a92967834bf0e64ca1205db4680d04048
Gitweb:        https://git.kernel.org/tip/3ea1704a92967834bf0e64ca1205db4680d04048
Author:        Thomas Gleixner <tglx@xxxxxxxxxxxxx>
AuthorDate:    Thu, 07 Dec 2023 20:49:24 +01:00
Committer:     Borislav Petkov (AMD) <bp@xxxxxxxxx>
CommitterDate: Fri, 15 Dec 2023 19:34:42 +01:00

x86/alternatives: Sync core before enabling interrupts

text_poke_early() does:

   local_irq_save(flags);
   memcpy(addr, opcode, len);
   local_irq_restore(flags);
   sync_core();

That's not really correct because the synchronization should happen before
interrupts are re-enabled to ensure that a pending interrupt observes the
complete update of the opcodes.

It's not entirely clear whether the interrupt entry provides enough
serialization already, but moving the sync_core() invocation into interrupt
disabled region does no harm and is obviously correct.

Fixes: 6fffacb30349 ("x86/alternatives, jumplabel: Use text_poke_early() before mm_init()")
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Borislav Petkov (AMD) <bp@xxxxxxxxx>
Acked-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Cc: <stable@xxxxxxxxxx>
Link: https://lore.kernel.org/r/ZT6narvE%2BLxX%2B7Be@xxxxxxxxxxxxx
---
 arch/x86/kernel/alternative.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index 73be393..fd44739 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -1685,8 +1685,8 @@ void __init_or_module text_poke_early(void *addr, const void *opcode,
 	} else {
 		local_irq_save(flags);
 		memcpy(addr, opcode, len);
-		local_irq_restore(flags);
 		sync_core();
+		local_irq_restore(flags);
 
 		/*
 		 * Could also do a CLFLUSH here to speed up CPU recovery; but