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SubjectRe: [PATCH 4/6] hw_breakpoint: Factor out __modify_user_hw_breakpoint function
On Mon, Nov 27, 2017 at 05:21:31PM +0100, Jiri Olsa wrote:
> +static int __modify_user_hw_breakpoint(struct perf_event *bp, struct perf_event_attr *attr)
> +{
> + u64 old_addr = bp->attr.bp_addr;
> + u64 old_len = bp->attr.bp_len;
> + int old_type = bp->attr.bp_type;
> + bool modify = attr->bp_type != old_type;
> + int err = 0;
> +
> + bp->attr.bp_addr = attr->bp_addr;
> + bp->attr.bp_type = attr->bp_type;
> + bp->attr.bp_len = attr->bp_len;
> +
> + err = validate_hw_breakpoint(bp);
> + if (!err && modify)
> + err = modify_bp_slot(bp, old_type);
> +
> + if (err) {
> + bp->attr.bp_addr = old_addr;
> + bp->attr.bp_type = old_type;
> + bp->attr.bp_len = old_len;
> + return err;
> + }
> +
> + bp->attr.disabled = attr->disabled;
> + return 0;
> +}

I think this function is failing to check if anything else in the attr
changes.

For example, someone could have added PERF_SAMPLE_BRANCH_STACK. That's
something you'll fail to create breakpoints with, but this modification
would 'accept'.

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