Messages in this thread | | | Date | Thu, 1 Aug 2019 13:16:22 +0100 | From | Will Deacon <> | Subject | Re: [PATCH v3 1/4] arm64: kprobes: Recover pstate.D in single-step exception handler |
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On Thu, Jul 25, 2019 at 05:15:54PM +0900, Masami Hiramatsu wrote: > kprobes manipulates the interrupted PSTATE for single step, and > doesn't restore it. Thus, if we put a kprobe where the pstate.D > (debug) masked, the mask will be cleared after the kprobe hits. > > Moreover, in the most complicated case, this can lead a kernel > crash with below message when a nested kprobe hits. > > [ 152.118921] Unexpected kernel single-step exception at EL1 > > When the 1st kprobe hits, do_debug_exception() will be called. > At this point, debug exception (= pstate.D) must be masked (=1). > But if another kprobes hits before single-step of the first kprobe > (e.g. inside user pre_handler), it unmask the debug exception > (pstate.D = 0) and return. > Then, when the 1st kprobe setting up single-step, it saves current > DAIF, mask DAIF, enable single-step, and restore DAIF. > However, since "D" flag in DAIF is cleared by the 2nd kprobe, the > single-step exception happens soon after restoring DAIF. > > This has been introduced by commit 7419333fa15e ("arm64: kprobe: > Always clear pstate.D in breakpoint exception handler") > > To solve this issue, this stores all DAIF bits and restore it > after single stepping. > > Reported-by: Naresh Kamboju <naresh.kamboju@linaro.org> > Fixes: commit 7419333fa15e ("arm64: kprobe: Always clear pstate.D in breakpoint exception handler") > Reviewed-by: James Morse <james.morse@arm.com> > Tested-by: James Morse <james.morse@arm.com> > Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org> > --- > Changes in v3: > - Update patch description > - move PSR_DAIF_MASK in daifflags.h > Changes in v2: > - Save and restore all DAIF flags. > - Operate pstate directly and remove spsr_set_debug_flag(). > --- > arch/arm64/include/asm/daifflags.h | 2 ++ > arch/arm64/kernel/probes/kprobes.c | 39 +++++------------------------------- > 2 files changed, 7 insertions(+), 34 deletions(-)
I'm seeing an allmodconfig build failure with this:
arch/arm64/kernel/probes/kprobes.c: In function ‘kprobes_save_local_irqflag’: arch/arm64/kernel/probes/kprobes.c:181:38: error: ‘DAIF_MASK’ undeclared (first use in this function); did you mean ‘BIT_MASK’? kcb->saved_irqflag = regs->pstate & DAIF_MASK; ^~~~~~~~~ BIT_MASK arch/arm64/kernel/probes/kprobes.c:181:38: note: each undeclared identifier is reported only once for each function it appears in arch/arm64/kernel/probes/kprobes.c: In function ‘kprobes_restore_local_irqflag’: arch/arm64/kernel/probes/kprobes.c:190:19: error: ‘DAIF_MASK’ undeclared (first use in this function); did you mean ‘BIT_MASK’? regs->pstate &= ~DAIF_MASK; ^~~~~~~~~ BIT_MASK make[2]: *** [scripts/Makefile.build:274: arch/arm64/kernel/probes/kprobes.o] Error 1
Will
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