Messages in this thread | | | Date | Thu, 1 Aug 2019 23:08:18 +0900 | From | Masami Hiramatsu <> | Subject | Re: [PATCH v3 1/4] arm64: kprobes: Recover pstate.D in single-step exception handler |
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On Thu, 1 Aug 2019 13:16:22 +0100 Will Deacon <will@kernel.org> wrote:
> 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
Oops, daifflags.h is included via kvm_host.h... OK, kprobes.c must include daifflags.h directly in this case.
I'll update this patch too.
Thank you,
> > Will
-- Masami Hiramatsu <mhiramat@kernel.org>
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