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Subject[tip:perf/core] hw_breakpoint: Add perf_event_attr fields check in __modify_user_hw_breakpoint()
Commit-ID:  705feaf321c37e4dca3637fd5cb3b275f17a06c9
Gitweb: https://git.kernel.org/tip/705feaf321c37e4dca3637fd5cb3b275f17a06c9
Author: Jiri Olsa <jolsa@kernel.org>
AuthorDate: Mon, 12 Mar 2018 14:45:45 +0100
Committer: Ingo Molnar <mingo@kernel.org>
CommitDate: Tue, 13 Mar 2018 06:56:08 +0100

hw_breakpoint: Add perf_event_attr fields check in __modify_user_hw_breakpoint()

And rename it to modify_user_hw_breakpoint_check().

We are about to use modify_user_hw_breakpoint_check() for user space
breakpoints modification, we must be very strict to check only the
fields we can change have changed. As Peter explained:

"Suppose someone does:

attr = malloc(sizeof(*attr)); // uninitialized memory
attr->type = BP;
attr->bp_addr = new_addr;
attr->bp_type = bp_type;
attr->bp_len = bp_len;
ioctl(fd, PERF_IOC_MOD_ATTR, &attr);

And feeds absolute shite for the rest of the fields.
Then we later want to extend IOC_MOD_ATTR to allow changing
attr::sample_type but we can't, because that would break the
above application."

I'm making this check optional because we already export
modify_user_hw_breakpoint() and with this check we could
break existing users.

Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Hari Bathini <hbathini@linux.vnet.ibm.com>
Cc: Jin Yao <yao.jin@linux.intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Kan Liang <kan.liang@intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Milind Chabbi <chabbi.milind@gmail.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Oleg Nesterov <onestero@redhat.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will.deacon@arm.com>
Link: http://lkml.kernel.org/r/20180312134548.31532-6-jolsa@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
kernel/events/hw_breakpoint.c | 9 +++++++--
1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/kernel/events/hw_breakpoint.c b/kernel/events/hw_breakpoint.c
index a556aba223da..0c82663395f7 100644
--- a/kernel/events/hw_breakpoint.c
+++ b/kernel/events/hw_breakpoint.c
@@ -456,7 +456,9 @@ register_user_hw_breakpoint(struct perf_event_attr *attr,
}
EXPORT_SYMBOL_GPL(register_user_hw_breakpoint);

-static int __modify_user_hw_breakpoint(struct perf_event *bp, struct perf_event_attr *attr)
+static int
+modify_user_hw_breakpoint_check(struct perf_event *bp, struct perf_event_attr *attr,
+ bool check)
{
u64 old_addr = bp->attr.bp_addr;
u64 old_len = bp->attr.bp_len;
@@ -468,6 +470,9 @@ static int __modify_user_hw_breakpoint(struct perf_event *bp, struct perf_event_
bp->attr.bp_type = attr->bp_type;
bp->attr.bp_len = attr->bp_len;

+ if (check && memcmp(&bp->attr, attr, sizeof(*attr)))
+ return -EINVAL;
+
err = validate_hw_breakpoint(bp);
if (!err && modify)
err = modify_bp_slot(bp, old_type);
@@ -505,7 +510,7 @@ int modify_user_hw_breakpoint(struct perf_event *bp, struct perf_event_attr *att
else
perf_event_disable(bp);

- err = __modify_user_hw_breakpoint(bp, attr);
+ err = modify_user_hw_breakpoint_check(bp, attr, false);

if (err) {
if (!bp->attr.disabled)
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