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Subject[PATCH 03/13] perf/hw_breakpoint: Modify breakpoint even if the new attr has disabled set
Date
From: Jiri Olsa <jolsa@kernel.org>

We need to change the breakpoint even if the attr with new fields has
disabled set to true.

Current code prevents following user code to change the breakpoint
address:

ptrace(PTRACE_POKEUSER, child, offsetof(struct user, u_debugreg[0]), addr_1)
ptrace(PTRACE_POKEUSER, child, offsetof(struct user, u_debugreg[0]), addr_2)
ptrace(PTRACE_POKEUSER, child, offsetof(struct user, u_debugreg[7]), dr7)

The first PTRACE_POKEUSER creates the breakpoint with attr.disabled set
to true:

ptrace_set_breakpoint_addr(nr = 0)
struct perf_event *bp = t->ptrace_bps[nr];

ptrace_register_breakpoint(..., disabled = true)
ptrace_fill_bp_fields(..., disabled)
register_user_hw_breakpoint

So the second PTRACE_POKEUSER will be omitted:

ptrace_set_breakpoint_addr(nr = 0)
struct perf_event *bp = t->ptrace_bps[nr];
struct perf_event_attr attr = bp->attr;

modify_user_hw_breakpoint(bp, &attr)
if (!attr->disabled)
modify_user_hw_breakpoint_check

Reported-by: Milind Chabbi <chabbi.milind@gmail.com>
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Acked-by: Frederic Weisbecker <frederic@kernel.org>
Acked-by: Oleg Nesterov <oleg@redhat.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20180827091228.2878-3-jolsa@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
---
kernel/events/hw_breakpoint.c | 10 ++++++----
1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/kernel/events/hw_breakpoint.c b/kernel/events/hw_breakpoint.c
index b3814fce5ecb..fb229d9c7f3c 100644
--- a/kernel/events/hw_breakpoint.c
+++ b/kernel/events/hw_breakpoint.c
@@ -509,6 +509,8 @@ modify_user_hw_breakpoint_check(struct perf_event *bp, struct perf_event_attr *a
*/
int modify_user_hw_breakpoint(struct perf_event *bp, struct perf_event_attr *attr)
{
+ int err;
+
/*
* modify_user_hw_breakpoint can be invoked with IRQs disabled and hence it
* will not be possible to raise IPIs that invoke __perf_event_disable.
@@ -520,11 +522,11 @@ int modify_user_hw_breakpoint(struct perf_event *bp, struct perf_event_attr *att
else
perf_event_disable(bp);

- if (!attr->disabled) {
- int err = modify_user_hw_breakpoint_check(bp, attr, false);
+ err = modify_user_hw_breakpoint_check(bp, attr, false);
+ if (err)
+ return err;

- if (err)
- return err;
+ if (!attr->disabled) {
perf_event_enable(bp);
bp->attr.disabled = 0;
}
--
2.14.4
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