Commit 3f74306a authored Dec 22, 2015 by Rob Gardner Committed by David S. Miller Dec 24, 2015

sparc64: Ensure perf can access user stacks



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>

parent 1ca04a4c

arch/sparc/kernel/perf_event.c

+7 −0

Original line number	Diff line number	Diff line
		@@ -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);
		}