On Fri, Aug 10, 2018 at 12:47:27PM +0200, Jiri Olsa wrote: > 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 > > Acked-by: Oleg Nesterov <o...@redhat.com> > Reported-by: Milind Chabbi <chabbi.mil...@gmail.com> > Link: http://lkml.kernel.org/n/tip-yjhgplc28gk5gfzt7ceoo...@git.kernel.org > Signed-off-by: Jiri Olsa <jo...@kernel.org>
Right, now that we fixed the breakpoint modification arch code, it should be safe to do that. Thanks! Acked-by: Frederic Weisbecker <frede...@kernel.org>
