Commit-ID:  705feaf321c37e4dca3637fd5cb3b275f17a06c9
Gitweb:     https://git.kernel.org/tip/705feaf321c37e4dca3637fd5cb3b275f17a06c9
Author:     Jiri Olsa <jo...@kernel.org>
AuthorDate: Mon, 12 Mar 2018 14:45:45 +0100
Committer:  Ingo Molnar <mi...@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 <pet...@infradead.org>
Signed-off-by: Jiri Olsa <jo...@kernel.org>
Cc: Alexander Shishkin <alexander.shish...@linux.intel.com>
Cc: Arnaldo Carvalho de Melo <a...@redhat.com>
Cc: David Ahern <dsah...@gmail.com>
Cc: Frederic Weisbecker <fweis...@gmail.com>
Cc: Hari Bathini <hbath...@linux.vnet.ibm.com>
Cc: Jin Yao <yao....@linux.intel.com>
Cc: Jiri Olsa <jo...@redhat.com>
Cc: Kan Liang <kan.li...@intel.com>
Cc: Linus Torvalds <torva...@linux-foundation.org>
Cc: Michael Ellerman <m...@ellerman.id.au>
Cc: Milind Chabbi <chabbi.mil...@gmail.com>
Cc: Namhyung Kim <namhy...@kernel.org>
Cc: Oleg Nesterov <onest...@redhat.com>
Cc: Peter Zijlstra <a.p.zijls...@chello.nl>
Cc: Sukadev Bhattiprolu <suka...@linux.vnet.ibm.com>
Cc: Thomas Gleixner <t...@linutronix.de>
Cc: Will Deacon <will.dea...@arm.com>
Link: http://lkml.kernel.org/r/20180312134548.31532-6-jo...@kernel.org
Signed-off-by: Ingo Molnar <mi...@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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