x86/split-lock: Avoid returning with interrupts enabled

BugLink: https://bugs.launchpad.net/bugs/1910109
commit e14fd4ba8fb47fcf5f244366ec01ae94490cd86a upstream.

When a split lock is detected always make sure to disable interrupts
before returning from the trap handler.

The kernel exit code assumes that all exits run with interrupts
disabled, otherwise the SWAPGS sequence can race against interrupts and
cause recursing page faults and later panics.

The problem will only happen on CPUs with split lock disable
functionality, so Icelake Server, Tiger Lake, Snow Ridge, Jacobsville.

Fixes: ca4c6a9858c2 ("x86/traps: Make interrupt enable/disable symmetric in C code")
Fixes: bce9b042ec73 ("x86/traps: Disable interrupts in exc_aligment_check()") # v5.8+
Signed-off-by: Andi Kleen <ak@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: Tony Luck <tony.luck@intel.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Paolo Pisati <paolo.pisati@canonical.com>

diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index e19df6cde35d1d5d7c6a1ffb09e2d26cc39d1b95..170c94ec00685de0348f39e8f1087f9e7f119fed 100644 (file)
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -299,11 +299,12 @@ DEFINE_IDTENTRY_ERRORCODE(exc_alignment_check)
        local_irq_enable();
 
        if (handle_user_split_lock(regs, error_code))
-               return;
+               goto out;
 
        do_trap(X86_TRAP_AC, SIGBUS, "alignment check", regs,
                error_code, BUS_ADRALN, NULL);
 
+out:
        local_irq_disable();
 }