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profiling: fix sampling step on 64-bit big-endian systems

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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: 2d186afd04 ("profiling: fix shift-out-of-bounds bugs")
Signed-off-by: Avi Weiss <thnkslprpt@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Bradley Morgan <brads@mainlining.org>
This commit is contained in:
Avi Weiss 2026-10-20 13:12:24 +03:00 committed by Andrew Morton
parent 66644b992f
commit b1d68946a0
1 changed files with 1 additions and 1 deletions
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2
kernel/profile.c
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@ -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;