From b1d68946a08313895f352af5336623d29739c299 Mon Sep 17 00:00:00 2001 From: Avi Weiss Date: Tue, 20 Oct 2026 13:12:24 +0300 Subject: [PATCH] profiling: fix sampling step on 64-bit big-endian systems 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@gmail.com Fixes: 2d186afd04d6 ("profiling: fix shift-out-of-bounds bugs") Signed-off-by: Avi Weiss Signed-off-by: Andrew Morton Reviewed-by: Bradley Morgan --- kernel/profile.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/profile.c b/kernel/profile.c index 1fcf1adcf4eb..e7defa90a34c 100644 --- a/kernel/profile.c +++ b/kernel/profile.c @@ -156,7 +156,7 @@ read_profile(struct file *file, char __user *buf, size_t count, loff_t *ppos) 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;