linux-kernel - [PATCH] tracing/user_events: Use long vs int for atomic bit ops

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Date:   Fri,  5 May 2023 13:58:55 -0700
From:   Beau Belgrave <beaub@...ux.microsoft.com>
To:     rostedt@...dmis.org, mhiramat@...nel.org
Cc:     linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
        dan.carpenter@...aro.org
Subject: [PATCH] tracing/user_events: Use long vs int for atomic bit ops

Each event stores a int to track which bit to set/clear when enablement
changes. On big endian 64-bit configurations, it's possible this could
cause memory corruption when it's used for atomic bit operations.

Use unsigned long for enablement values to ensure any possible
corruption cannot occur. Downcast to int after mask for the bit target.

Link: https://lore.kernel.org/all/6f758683-4e5e-41c3-9b05-9efc703e827c@kili.mountain/

Fixes: dcb8177c1395 ("tracing/user_events: Add ioctl for disabling addresses")
Reported-by: Dan Carpenter <dan.carpenter@...aro.org>
Signed-off-by: Beau Belgrave <beaub@...ux.microsoft.com>
---
 kernel/trace/trace_events_user.c | 15 ++++++++-------
 1 file changed, 8 insertions(+), 7 deletions(-)

diff --git a/kernel/trace/trace_events_user.c b/kernel/trace/trace_events_user.c
index b1ecd7677642..e37c7f168c44 100644
--- a/kernel/trace/trace_events_user.c
+++ b/kernel/trace/trace_events_user.c
@@ -101,7 +101,7 @@ struct user_event_enabler {
 	unsigned long		addr;
 
 	/* Track enable bit, flags, etc. Aligned for bitops. */
-	unsigned int		values;
+	unsigned long		values;
 };
 
 /* Bits 0-5 are for the bit to update upon enable/disable (0-63 allowed) */
@@ -116,7 +116,9 @@ struct user_event_enabler {
 /* Only duplicate the bit value */
 #define ENABLE_VAL_DUP_MASK ENABLE_VAL_BIT_MASK
 
-#define ENABLE_BITOPS(e) ((unsigned long *)&(e)->values)
+#define ENABLE_BITOPS(e) (&(e)->values)
+
+#define ENABLE_BIT(e) ((int)((e)->values & ENABLE_VAL_BIT_MASK))
 
 /* Used for asynchronous faulting in of pages */
 struct user_event_enabler_fault {
@@ -423,9 +425,9 @@ static int user_event_enabler_write(struct user_event_mm *mm,
 
 	/* Update bit atomically, user tracers must be atomic as well */
 	if (enabler->event && enabler->event->status)
-		set_bit(enabler->values & ENABLE_VAL_BIT_MASK, ptr);
+		set_bit(ENABLE_BIT(enabler), ptr);
 	else
-		clear_bit(enabler->values & ENABLE_VAL_BIT_MASK, ptr);
+		clear_bit(ENABLE_BIT(enabler), ptr);
 
 	kunmap_local(kaddr);
 	unpin_user_pages_dirty_lock(&page, 1, true);
@@ -440,8 +442,7 @@ static bool user_event_enabler_exists(struct user_event_mm *mm,
 	struct user_event_enabler *next;
 
 	list_for_each_entry_safe(enabler, next, &mm->enablers, link) {
-		if (enabler->addr == uaddr &&
-		    (enabler->values & ENABLE_VAL_BIT_MASK) == bit)
+		if (enabler->addr == uaddr && ENABLE_BIT(enabler) == bit)
 			return true;
 	}
 
@@ -2272,7 +2273,7 @@ static long user_events_ioctl_unreg(unsigned long uarg)
 
 	list_for_each_entry_safe(enabler, next, &mm->enablers, link)
 		if (enabler->addr == reg.disable_addr &&
-		    (enabler->values & ENABLE_VAL_BIT_MASK) == reg.disable_bit) {
+		    ENABLE_BIT(enabler) == reg.disable_bit) {
 			set_bit(ENABLE_VAL_FREEING_BIT, ENABLE_BITOPS(enabler));
 
 			if (!test_bit(ENABLE_VAL_FAULTING_BIT, ENABLE_BITOPS(enabler)))

base-commit: 3862f86c1529fa0016de6344eb974877b4cd3838
-- 
2.25.1