[tip: x86/urgent] x86/ioperm: Prevent NULL dereference on theoretical missing IO bitmap

[tip-bot2 for Li RongQing]

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

Commit-ID:     2d36d3b451a94899db9c965adde15492ffe6027a
Gitweb:        https://git.kernel.org/tip/2d36d3b451a94899db9c965adde15492ffe6027a
Author:        Li RongQing <lirongqing@xxxxxxxxx>
AuthorDate:    Mon, 15 Jun 2026 15:01:15 +08:00
Committer:     Ingo Molnar <mingo@xxxxxxxxxx>
CommitterDate: Mon, 15 Jun 2026 09:40:45 +02:00

x86/ioperm: Prevent NULL dereference on theoretical missing IO bitmap

Outside the IOPL emulation path, the IO bitmap is always expected
to be allocated when TIF_IO_BITMAP is set. The paranoid WARN_ON_ONCE()
handles the case where the flag and the pointer got out of sync.
In this theoretical scenario, which presumes some other bug in the
code that triggers the WARN_ON_ONCe(), return early, instead of
continuing and dereferencing a NULL pointer.

[ mingo: Clarified the changelog. ]

Signed-off-by: Li RongQing <lirongqing@xxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Reviewed-by: Sohil Mehta <sohil.mehta@xxxxxxxxx>
Cc: H. Peter Anvin <hpa@xxxxxxxxx>
Link: https://patch.msgid.link/20260615070115.4720-1-lirongqing@xxxxxxxxx
---
 arch/x86/kernel/process.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index 4c718f8..d5cd217 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -486,6 +486,7 @@ void native_tss_update_io_bitmap(void)
 		if (WARN_ON_ONCE(!iobm)) {
 			clear_thread_flag(TIF_IO_BITMAP);
 			native_tss_invalidate_io_bitmap();
+			return;
 		}
 
 		/*