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perf/x86: Use scoped user access for the user callchain frames

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The user callchain walkers read each two-word stack frame with
__get_user(), after checking the frame with valid_user_frame(), which is
just __access_ok().  They run with page faults disabled, since they can
be called from NMI context.

Read each frame inside a scoped_user_read_access() instead, which does
the range check itself and needs only a single stac/clac pair for both
loads.  That leaves valid_user_frame() unused, so remove it.

This is part of getting rid of __get_user() and __put_user() entirely.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Linus Torvalds 2026-10-19 19:23:44 -10:00
parent 7941b97fdd
commit 0f697d307c
1 changed files with 10 additions and 20 deletions
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30
arch/x86/events/core.c
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@ -2902,12 +2902,6 @@ perf_callchain_kernel(struct perf_callchain_entry_ctx *entry, struct pt_regs *re
}
}
static inline int
valid_user_frame(const void __user *fp, unsigned long size)
{
return __access_ok(fp, size);
}
static unsigned long get_segment_base(unsigned int segment)
{
struct desc_struct *desc;
@ -2971,17 +2965,15 @@ perf_callchain_user32(struct pt_regs *regs, struct perf_callchain_entry_ctx *ent
perf_callchain_store(entry, ret_addr);
while (entry->nr < entry->max_stack) {
if (!valid_user_frame(fp, sizeof(frame)))
break;
if (__get_user(frame.next_frame, &fp->next_frame))
break;
if (__get_user(frame.return_address, &fp->return_address))
break;
scoped_user_read_access(fp, out) {
unsafe_get_user(frame.next_frame, &fp->next_frame, out);
unsafe_get_user(frame.return_address, &fp->return_address, out);
}
perf_callchain_store(entry, cs_base + frame.return_address);
fp = compat_ptr(ss_base + frame.next_frame);
}
out:
pagefault_enable();
return 1;
}
@ -3036,17 +3028,15 @@ perf_callchain_user(struct perf_callchain_entry_ctx *entry, struct pt_regs *regs
perf_callchain_store(entry, ret_addr);
while (entry->nr < entry->max_stack) {
if (!valid_user_frame(fp, sizeof(frame)))
break;
if (__get_user(frame.next_frame, &fp->next_frame))
break;
if (__get_user(frame.return_address, &fp->return_address))
break;
scoped_user_read_access(fp, out) {
unsafe_get_user(frame.next_frame, &fp->next_frame, out);
unsafe_get_user(frame.return_address, &fp->return_address, out);
}
perf_callchain_store(entry, frame.return_address);
fp = (void __user *)frame.next_frame;
}
out:
pagefault_enable();
}