[PATCH 1/3] profiling: fix sampling step on 64-bit big-endian systems

[Andrew Morton]

From: Avi Weiss <thnkslprpt@xxxxxxxxx>
Subject: profiling: fix sampling step on 64-bit big-endian systems
Date: Tue, 20 Oct 2026 13:12:24 +0300

read_profile() stores the sampling step in an unsigned long but copies
only four bytes to userspace.  On 64-bit big-endian systems (not common
obviously), this copies the upper 32 bits and discards the rest, causing
/proc/profile to report zero for normal shift values.

Cast to unsigned int so we get the correct 4 bytes, while keeping the
shift calculation in unsigned long.

A small C reproducer under qemu-s390x reproduced this and proved the fix
works for prof_shift=2.

Link: https://lore.kernel.org/20261020101225.917959-1-thnkslprpt@xxxxxxxxx
Fixes: 2d186afd04d6 ("profiling: fix shift-out-of-bounds bugs")
Signed-off-by: Avi Weiss <thnkslprpt@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Reviewed-by: Bradley Morgan <brads@xxxxxxxxxxxxxx>
---

 kernel/profile.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/kernel/profile.c~profiling-fix-sampling-step-on-64-bit-big-endian-systems
+++ a/kernel/profile.c
@@ -156,7 +156,7 @@ read_profile(struct file *file, char __u
 	unsigned long p = *ppos;
 	ssize_t read;
 	char *pnt;
-	unsigned long sample_step = 1UL << prof_shift;
+	unsigned int sample_step = (unsigned int)(1UL << prof_shift);
 
 	if (p >= (prof_len+1)*sizeof(unsigned int))
 		return 0;
_