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* [PATCH 1/2] tracing/user_events: Handle ioctls from 32-bit tasks
@ 2026-09-28 17:14 Danish Khateeb
  2026-09-28 17:14 ` [PATCH 2/2] selftests/user_events: Fix pointer casts for 32-bit builds Danish Khateeb
  0 siblings, 1 reply; 2+ messages in thread
From: Danish Khateeb @ 2026-09-28 17:14 UTC (permalink / raw)
  To: Steven Rostedt, Masami Hiramatsu
  Cc: Mathieu Desnoyers, Beau Belgrave, Shuah Khan, linux-trace-kernel,
	linux-kselftest, linux-kernel, Danish Khateeb, stable

The DIAG_IOCSREG, DIAG_IOCSDEL and DIAG_IOCSUNREG ioctl numbers are
defined with pointer types, so their size field is 4 for 32-bit
userspace and 8 for 64-bit userspace. user_events_data has no
compat_ioctl handler, so on a 64-bit kernel every one of these ioctls
from a 32-bit task fails with -ENOTTY and such a task cannot register
any user events.

struct user_reg and struct user_unreg are packed and only use fixed-size
fields, so they have the same layout for 32-bit and 64-bit tasks. Add a
compat_ioctl handler that maps the 32-bit ioctl numbers to the native
ones and passes the argument through compat_ptr().

Fixes: 7f5a08c79df3 ("user_events: Add minimal support for trace_event into ftrace")
Cc: stable@vger.kernel.org
Assisted-by: LLM
Signed-off-by: Danish Khateeb <danishkhateeb03@gmail.com>
---

Notes:
    Tested on x86_64 in QEMU (v7.3-rc5 plus this series, KASAN and lockdep):
    - A 32-bit program that registers and unregisters an event gets -ENOTTY
      from DIAG_IOCSREG before and works after.
    - tools/testing/selftests/user_events built with -m32 (with 2/2): all
      four tests fail before and pass after, in three runs each. The
      64-bit build passes before and after. No splats.
    Also built with CONFIG_COMPAT=n on x86_64 and with CONFIG_COMPAT=y on
    riscv64, both with W=1.

 kernel/trace/trace_events_user.c | 32 ++++++++++++++++++++++++++++++++
 1 file changed, 32 insertions(+)

diff --git a/kernel/trace/trace_events_user.c b/kernel/trace/trace_events_user.c
index f658c3a77aa7..07cfbb5a17de 100644
--- a/kernel/trace/trace_events_user.c
+++ b/kernel/trace/trace_events_user.c
@@ -8,6 +8,7 @@
 
 #include <linux/bitmap.h>
 #include <linux/cdev.h>
+#include <linux/compat.h>
 #include <linux/hashtable.h>
 #include <linux/list.h>
 #include <linux/io.h>
@@ -2737,6 +2738,36 @@ static long user_events_ioctl(struct file *file, unsigned int cmd,
 	return ret;
 }
 
+#ifdef CONFIG_COMPAT
+/*
+ * These IOCTLs encode the size of a pointer and thus change their numbers
+ * between 32 and 64 bits. The structs they point to have the same layout.
+ */
+#define DIAG_IOCSREG_COMPAT	_IOWR(DIAG_IOC_MAGIC, 0, compat_uptr_t)
+#define DIAG_IOCSDEL_COMPAT	_IOW(DIAG_IOC_MAGIC, 1, compat_uptr_t)
+#define DIAG_IOCSUNREG_COMPAT	_IOW(DIAG_IOC_MAGIC, 2, compat_uptr_t)
+
+static long user_events_compat_ioctl(struct file *file, unsigned int cmd,
+				     unsigned long uarg)
+{
+	switch (cmd) {
+	case DIAG_IOCSREG_COMPAT:
+		cmd = DIAG_IOCSREG;
+		break;
+	case DIAG_IOCSDEL_COMPAT:
+		cmd = DIAG_IOCSDEL;
+		break;
+	case DIAG_IOCSUNREG_COMPAT:
+		cmd = DIAG_IOCSUNREG;
+		break;
+	}
+
+	return user_events_ioctl(file, cmd, (unsigned long)compat_ptr(uarg));
+}
+#else
+#define user_events_compat_ioctl NULL
+#endif
+
 /*
  * Handles the final close of the file from user mode.
  */
@@ -2787,6 +2818,7 @@ static const struct file_operations user_data_fops = {
 	.write		= user_events_write,
 	.write_iter	= user_events_write_iter,
 	.unlocked_ioctl	= user_events_ioctl,
+	.compat_ioctl	= user_events_compat_ioctl,
 	.release	= user_events_release,
 };
 

base-commit: 72d3fcf802c45d00b300f25b848a93c3a2bd7c7e
-- 
2.55.0


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2026-09-28 17:14 [PATCH 1/2] tracing/user_events: Handle ioctls from 32-bit tasks Danish Khateeb
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