| Message ID | 20180827185631.163506-2-jannh@google.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | x86: BUG() on #GP / kernel #PF in uaccess | expand |
On Mon, Aug 27, 2018 at 08:56:25PM +0200, Jann Horn wrote: > This is an extension of commit b506a9d08bae ("x86: code clarification patch > to Kprobes arch code"). As that commit explains, even though > kprobe_running() can't be called with preemption enabled, you don't have to > disable preemption - if preemption is on, you can't be in a kprobe. > > Also, use X86_TRAP_PF instead of 14. > > Signed-off-by: Jann Horn <jannh@google.com> > --- > arch/x86/mm/fault.c | 19 ++++++++----------- > 1 file changed, 8 insertions(+), 11 deletions(-) > > diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c > index b9123c497e0a..2254a30533b9 100644 > --- a/arch/x86/mm/fault.c > +++ b/arch/x86/mm/fault.c > @@ -44,17 +44,14 @@ kmmio_fault(struct pt_regs *regs, unsigned long addr) > > static nokprobe_inline int kprobes_fault(struct pt_regs *regs) > { > - int ret = 0; > - > - /* kprobe_running() needs smp_processor_id() */ > - if (kprobes_built_in() && !user_mode(regs)) { > - preempt_disable(); > - if (kprobe_running() && kprobe_fault_handler(regs, 14)) > - ret = 1; > - preempt_enable(); > - } > - > - return ret; > + /* > + * To be potentially processing a kprobe fault and to be allowed to call > + * kprobe_running(), we have to be non-preemptible. > + */ > + if (kprobes_built_in() && !user_mode(regs) && !preemptible() && > + kprobe_running() && kprobe_fault_handler(regs, X86_TRAP_PF)) > + return 1; > + return 0; Maybe even: return (kprobes_built_in() && !user_mode(regs) && !preemptible() && kprobe_running() && kprobe_fault_handler(regs, X86_TRAP_PF)); Although I'd do it a bit more readable by flipping the checks and splitting them: if (!kprobes_built_in()) return 0; if (user_mode(regs)) return 0; ... return kprobe_fault_handler(regs, X86_TRAP_PF); }
diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c index b9123c497e0a..2254a30533b9 100644 --- a/arch/x86/mm/fault.c +++ b/arch/x86/mm/fault.c @@ -44,17 +44,14 @@ kmmio_fault(struct pt_regs *regs, unsigned long addr) static nokprobe_inline int kprobes_fault(struct pt_regs *regs) { - int ret = 0; - - /* kprobe_running() needs smp_processor_id() */ - if (kprobes_built_in() && !user_mode(regs)) { - preempt_disable(); - if (kprobe_running() && kprobe_fault_handler(regs, 14)) - ret = 1; - preempt_enable(); - } - - return ret; + /* + * To be potentially processing a kprobe fault and to be allowed to call + * kprobe_running(), we have to be non-preemptible. + */ + if (kprobes_built_in() && !user_mode(regs) && !preemptible() && + kprobe_running() && kprobe_fault_handler(regs, X86_TRAP_PF)) + return 1; + return 0; } /*
This is an extension of commit b506a9d08bae ("x86: code clarification patch to Kprobes arch code"). As that commit explains, even though kprobe_running() can't be called with preemption enabled, you don't have to disable preemption - if preemption is on, you can't be in a kprobe. Also, use X86_TRAP_PF instead of 14. Signed-off-by: Jann Horn <jannh@google.com> --- arch/x86/mm/fault.c | 19 ++++++++----------- 1 file changed, 8 insertions(+), 11 deletions(-)