Messages in this thread | ![/](/images/icornerl.gif) | | Subject | Re: [PATCH v11 7/9] arm64: Add trampoline code for kretprobes | From | David Long <> | Date | Mon, 21 Mar 2016 09:30:43 -0400 |
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On 03/13/2016 09:52 AM, Marc Zyngier wrote: > On Wed, 9 Mar 2016 00:32:21 -0500 > David Long <dave.long@linaro.org> wrote: > > David, > > I remember looking at that code over your shoulder whilst at Connect > last week, but I clearly wasn't running on all cylinders, because there > is a few gotchas here - see below. > >> From: William Cohen <wcohen@redhat.com> >> >> The trampoline code is used by kretprobes to capture a return from a probed >> function. This is done by saving the registers, calling the handler, and >> restoring the registers. The code then returns to the original saved caller >> return address. It is necessary to do this directly instead of using a >> software breakpoint because the code used in processing that breakpoint >> could itself be kprobe'd and cause a problematic reentry into the debug >> exception handler. >> >> Signed-off-by: William Cohen <wcohen@redhat.com> >> Signed-off-by: David A. Long <dave.long@linaro.org> >> --- >> arch/arm64/include/asm/kprobes.h | 2 + >> arch/arm64/kernel/Makefile | 1 + >> arch/arm64/kernel/asm-offsets.c | 11 +++++ >> arch/arm64/kernel/kprobes.c | 5 ++ >> arch/arm64/kernel/kprobes_trampoline.S | 88 ++++++++++++++++++++++++++++++++++ >> 5 files changed, 107 insertions(+) >> create mode 100644 arch/arm64/kernel/kprobes_trampoline.S >> >> diff --git a/arch/arm64/include/asm/kprobes.h b/arch/arm64/include/asm/kprobes.h >> index 79c9511..61b4915 100644 >> --- a/arch/arm64/include/asm/kprobes.h >> +++ b/arch/arm64/include/asm/kprobes.h >> @@ -56,5 +56,7 @@ int kprobe_exceptions_notify(struct notifier_block *self, >> unsigned long val, void *data); >> int kprobe_breakpoint_handler(struct pt_regs *regs, unsigned int esr); >> int kprobe_single_step_handler(struct pt_regs *regs, unsigned int esr); >> +void kretprobe_trampoline(void); >> +void __kprobes *trampoline_probe_handler(struct pt_regs *regs); >> >> #endif /* _ARM_KPROBES_H */ >> diff --git a/arch/arm64/kernel/Makefile b/arch/arm64/kernel/Makefile >> index 08325e5..f192b7d 100644 >> --- a/arch/arm64/kernel/Makefile >> +++ b/arch/arm64/kernel/Makefile >> @@ -37,6 +37,7 @@ arm64-obj-$(CONFIG_CPU_IDLE) += cpuidle.o >> arm64-obj-$(CONFIG_JUMP_LABEL) += jump_label.o >> arm64-obj-$(CONFIG_KGDB) += kgdb.o >> arm64-obj-$(CONFIG_KPROBES) += kprobes.o kprobes-arm64.o \ >> + kprobes_trampoline.o \ >> probes-simulate-insn.o >> arm64-obj-$(CONFIG_EFI) += efi.o efi-entry.stub.o >> arm64-obj-$(CONFIG_PCI) += pci.o >> diff --git a/arch/arm64/kernel/asm-offsets.c b/arch/arm64/kernel/asm-offsets.c >> index fffa4ac6..f7cc8ce 100644 >> --- a/arch/arm64/kernel/asm-offsets.c >> +++ b/arch/arm64/kernel/asm-offsets.c >> @@ -50,6 +50,17 @@ int main(void) >> DEFINE(S_X5, offsetof(struct pt_regs, regs[5])); >> DEFINE(S_X6, offsetof(struct pt_regs, regs[6])); >> DEFINE(S_X7, offsetof(struct pt_regs, regs[7])); >> + DEFINE(S_X8, offsetof(struct pt_regs, regs[8])); >> + DEFINE(S_X10, offsetof(struct pt_regs, regs[10])); >> + DEFINE(S_X12, offsetof(struct pt_regs, regs[12])); >> + DEFINE(S_X14, offsetof(struct pt_regs, regs[14])); >> + DEFINE(S_X16, offsetof(struct pt_regs, regs[16])); >> + DEFINE(S_X18, offsetof(struct pt_regs, regs[18])); >> + DEFINE(S_X20, offsetof(struct pt_regs, regs[20])); >> + DEFINE(S_X22, offsetof(struct pt_regs, regs[22])); >> + DEFINE(S_X24, offsetof(struct pt_regs, regs[24])); >> + DEFINE(S_X26, offsetof(struct pt_regs, regs[26])); >> + DEFINE(S_X28, offsetof(struct pt_regs, regs[28])); >> DEFINE(S_LR, offsetof(struct pt_regs, regs[30])); >> DEFINE(S_SP, offsetof(struct pt_regs, sp)); >> #ifdef CONFIG_COMPAT >> diff --git a/arch/arm64/kernel/kprobes.c b/arch/arm64/kernel/kprobes.c >> index ffc5affd..bd3f233 100644 >> --- a/arch/arm64/kernel/kprobes.c >> +++ b/arch/arm64/kernel/kprobes.c >> @@ -532,6 +532,11 @@ int __kprobes longjmp_break_handler(struct kprobe *p, struct pt_regs *regs) >> return 1; >> } >> >> +void __kprobes __used *trampoline_probe_handler(struct pt_regs *regs) >> +{ >> + return NULL; >> +} >> + >> int __init arch_init_kprobes(void) >> { >> return 0; >> diff --git a/arch/arm64/kernel/kprobes_trampoline.S b/arch/arm64/kernel/kprobes_trampoline.S >> new file mode 100644 >> index 0000000..072b4e5 >> --- /dev/null >> +++ b/arch/arm64/kernel/kprobes_trampoline.S >> @@ -0,0 +1,88 @@ >> +/* >> + * trampoline entry and return code for kretprobes. >> + */ >> + >> +#include <linux/linkage.h> >> +#include <asm/asm-offsets.h> >> +#include <asm/assembler.h> >> + >> + .text >> + >> +.macro save_all_base_regs ctxt >> + stp x0, x1, [\ctxt, #S_X0] >> + stp x2, x3, [\ctxt, #S_X2] >> + stp x4, x5, [\ctxt, #S_X4] >> + stp x6, x7, [\ctxt, #S_X6] >> + stp x8, x9, [\ctxt, #S_X8] >> + stp x10, x11, [\ctxt, #S_X10] >> + stp x12, x13, [\ctxt, #S_X12] >> + stp x14, x15, [\ctxt, #S_X14] >> + stp x16, x17, [\ctxt, #S_X16] >> + stp x18, x19, [\ctxt, #S_X18] >> + stp x20, x21, [\ctxt, #S_X20] >> + stp x22, x23, [\ctxt, #S_X22] >> + stp x24, x25, [\ctxt, #S_X24] >> + stp x26, x27, [\ctxt, #S_X26] >> + stp x28, x29, [\ctxt, #S_X28] >> + str lr, [\ctxt, #S_LR] >> + add x0, \ctxt, #S_FRAME_SIZE >> + str x0, [\ctxt, #S_SP] > > Nit: this could also be rewritten as: > > add x0, \ctxt, #S_FRAME_SIZE > stp lr, xo, [\ctxt, #S_LR] > > Another thing worth noting is that since your macro saves all the > GP registers, only SP can be used for the ctxt parameter. This means > you're better off hardcoding SP in this macro, and not give the > illusion of being generic. >
OK.
>> +/* >> + * Construct a useful saved PSTATE >> + */ >> + mrs x0, nzcv >> + and x0, x0, #0xf0000000 > > It'd be worth spelling this as (PSR_N_BIT | PSR_Z_BIT | PSR_C_BIT | > PSR_V_BIT)... >
OK.
>> + mrs x1, daif >> + and x1, x1, #0x3c0 > > ... and this as (PSR_D_BIT | PSR_A_BIT | PSR_I_BIT | PSR_F_BIT). >
OK.
>> + orr x0, x0, x1 >> + mrs x1, CurrentEL >> + and x1, x1, #12 > > I'd like this '12' to be a bit more explicit. How about (3 << 2)? I > tend to parse this kind of things much more easily... >
OK.
>> + lsl x1, x1, #21 > > What's that shift for? The various bits should be at the right place > already. >
At the time it made sense, but rereading the ARM ARM it's not making so much sense.
>> + orr x0, x1, x0 >> + mrs x1, SPSel >> + and x1, x1, #1 >> + lsl x1, x1, #21 > > Same here (you're in single-step territory, which is probably not what > you want...). >
See previous comment.
>> + orr x0, x1, x0 >> + str x0, [\ctxt, #S_PSTATE] >> +.endm >> + >> +.macro restore_all_base_regs ctxt > > Same remark about the pseudo-generic parameter. >
OK.
>> + ldr x0, [\ctxt, #S_PSTATE] >> + and x0, x0, #0xf0000000 > > Same remark about using the PSR_* macros. >
OK.
>> + msr nzcv, x0 >> + ldp x0, x1, [\ctxt, #S_X0] >> + ldp x2, x3, [\ctxt, #S_X2] >> + ldp x4, x5, [\ctxt, #S_X4] >> + ldp x6, x7, [\ctxt, #S_X6] >> + ldp x8, x9, [\ctxt, #S_X8] >> + ldp x10, x11, [\ctxt, #S_X10] >> + ldp x12, x13, [\ctxt, #S_X12] >> + ldp x14, x15, [\ctxt, #S_X14] >> + ldp x16, x17, [\ctxt, #S_X16] >> + ldp x18, x19, [\ctxt, #S_X18] >> + ldp x20, x21, [\ctxt, #S_X20] >> + ldp x22, x23, [\ctxt, #S_X22] >> + ldp x24, x25, [\ctxt, #S_X24] >> + ldp x26, x27, [\ctxt, #S_X26] >> + ldp x28, x29, [\ctxt, #S_X28] >> +.endm >> + >> +ENTRY(kretprobe_trampoline) >> + >> + sub sp, sp, #S_FRAME_SIZE >> + >> + save_all_base_regs sp >> + >> + mov x0, sp >> + bl trampoline_probe_handler >> + /* Replace trampoline address in lr with actual >> + orig_ret_addr return address. */ >> + mov lr, x0 >> + >> + restore_all_base_regs sp >> + >> + add sp, sp, #S_FRAME_SIZE >> + >> + ret >> + >> +ENDPROC(kretprobe_trampoline) > > Thanks, > > M. >
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