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sparc64: Ensure perf can access user stacks

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When an interrupt (such as a perf counter interrupt) is delivered
while executing in user space, the trap entry code puts ASI_AIUS in
%asi so that copy_from_user() and copy_to_user() will access the
correct memory. But if a perf counter interrupt is delivered while the
cpu is already executing in kernel space, then the trap entry code
will put ASI_P in %asi, and this will prevent copy_from_user() from
reading any useful stack data in either of the perf_callchain_user_X
functions, and thus no user callgraph data will be collected for this
sample period. An additional problem is that a fault is guaranteed
to occur, and though it will be silently covered up, it wastes time
and could perturb state.

In perf_callchain_user(), we ensure that %asi contains ASI_AIUS
because we know for a fact that the subsequent calls to
copy_from_user() are intended to read the user's stack.

[ Use get_fs()/set_fs() -DaveM ]

Signed-off-by: Rob Gardner <rob.gardner@oracle.com>
Signed-off-by: Dave Aldridge <david.j.aldridge@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Rob Gardner 2015-12-22 21:16:06 -07:00 committed by David S. Miller
parent 1ca04a4ce0
commit 3f74306ac8
1 changed files with 7 additions and 0 deletions
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7
arch/sparc/kernel/perf_event.c
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@ -1828,11 +1828,16 @@ static void perf_callchain_user_32(struct perf_callchain_entry *entry,
void
perf_callchain_user(struct perf_callchain_entry *entry, struct pt_regs *regs)
{
mm_segment_t old_fs;
perf_callchain_store(entry, regs->tpc);
if (!current->mm)
return;
old_fs = get_fs();
set_fs(USER_DS);
flushw_user();
pagefault_disable();
@ -1843,4 +1848,6 @@ perf_callchain_user(struct perf_callchain_entry *entry, struct pt_regs *regs)
perf_callchain_user_64(entry, regs);
pagefault_enable();
set_fs(old_fs);
}