| Message ID | 156404255444.2020.3301023170351823334.stgit@devnote2 (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | arm64: kprobes: Fix some bugs in arm64 kprobes | expand |
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
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
diff --git a/arch/arm64/include/asm/daifflags.h b/arch/arm64/include/asm/daifflags.h index 987926ed535e..063c964af705 100644 --- a/arch/arm64/include/asm/daifflags.h +++ b/arch/arm64/include/asm/daifflags.h @@ -13,6 +13,8 @@ #define DAIF_PROCCTX 0 #define DAIF_PROCCTX_NOIRQ PSR_I_BIT #define DAIF_ERRCTX (PSR_I_BIT | PSR_A_BIT) +#define DAIF_MASK (PSR_D_BIT | PSR_A_BIT | PSR_I_BIT | PSR_F_BIT) + /* mask/save/unmask/restore all exceptions, including interrupts. */ static inline void local_daif_mask(void) diff --git a/arch/arm64/kernel/probes/kprobes.c b/arch/arm64/kernel/probes/kprobes.c index bd5dfffca272..bf2259651b67 100644 --- a/arch/arm64/kernel/probes/kprobes.c +++ b/arch/arm64/kernel/probes/kprobes.c @@ -167,33 +167,6 @@ static void __kprobes set_current_kprobe(struct kprobe *p) __this_cpu_write(current_kprobe, p); } -/* - * When PSTATE.D is set (masked), then software step exceptions can not be - * generated. - * SPSR's D bit shows the value of PSTATE.D immediately before the - * exception was taken. PSTATE.D is set while entering into any exception - * mode, however software clears it for any normal (none-debug-exception) - * mode in the exception entry. Therefore, when we are entering into kprobe - * breakpoint handler from any normal mode then SPSR.D bit is already - * cleared, however it is set when we are entering from any debug exception - * mode. - * Since we always need to generate single step exception after a kprobe - * breakpoint exception therefore we need to clear it unconditionally, when - * we become sure that the current breakpoint exception is for kprobe. - */ -static void __kprobes -spsr_set_debug_flag(struct pt_regs *regs, int mask) -{ - unsigned long spsr = regs->pstate; - - if (mask) - spsr |= PSR_D_BIT; - else - spsr &= ~PSR_D_BIT; - - regs->pstate = spsr; -} - /* * Interrupts need to be disabled before single-step mode is set, and not * reenabled until after single-step mode ends. @@ -205,17 +178,17 @@ spsr_set_debug_flag(struct pt_regs *regs, int mask) static void __kprobes kprobes_save_local_irqflag(struct kprobe_ctlblk *kcb, struct pt_regs *regs) { - kcb->saved_irqflag = regs->pstate; + kcb->saved_irqflag = regs->pstate & DAIF_MASK; regs->pstate |= PSR_I_BIT; + /* Unmask PSTATE.D for enabling software step exceptions. */ + regs->pstate &= ~PSR_D_BIT; } static void __kprobes kprobes_restore_local_irqflag(struct kprobe_ctlblk *kcb, struct pt_regs *regs) { - if (kcb->saved_irqflag & PSR_I_BIT) - regs->pstate |= PSR_I_BIT; - else - regs->pstate &= ~PSR_I_BIT; + regs->pstate &= ~DAIF_MASK; + regs->pstate |= kcb->saved_irqflag; } static void __kprobes @@ -252,8 +225,6 @@ static void __kprobes setup_singlestep(struct kprobe *p, set_ss_context(kcb, slot); /* mark pending ss */ - spsr_set_debug_flag(regs, 0); - /* IRQs and single stepping do not mix well. */ kprobes_save_local_irqflag(kcb, regs); kernel_enable_single_step(regs);
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(-)