Re: [PATCH] kernel/kprobes: Add test to validate pt_regs

From: Masami Hiramatsu
Date: Wed Jun 14 2017 - 01:50:32 EST

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In reply to: Masami Hiramatsu: "Re: [PATCH] kernel/kprobes: Add test to validate pt_regs"
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On Wed, 14 Jun 2017 11:40:08 +0900
Masami Hiramatsu <mhiramat@xxxxxxxxxx> wrote:

> On Fri, 9 Jun 2017 00:53:08 +0530
> "Naveen N. Rao" <naveen.n.rao@xxxxxxxxxxxxxxxxxx> wrote:
>
> > Add a test to verify that the registers passed in pt_regs on kprobe
> > (trap), optprobe (jump) and kprobe_on_ftrace (ftrace_caller) are
> > accurate. The tests are exercized if KPROBES_SANITY_TEST is enabled.
>
> Great!
>
> >
> > Implemented for powerpc64. Other architectures will have to implement
> > the relevant arch_* helpers and define HAVE_KPROBES_REGS_SANITY_TEST.
>
> Hmm, why don't you define that in arch/powerpc/Kconfig ?
> Also, could you split this into 3 patches for each case ?
>
> >
> > Signed-off-by: Naveen N. Rao <naveen.n.rao@xxxxxxxxxxxxxxxxxx>
> > ---
> > arch/powerpc/include/asm/kprobes.h | 4 +
> > arch/powerpc/lib/Makefile | 3 +-
> > arch/powerpc/lib/test_kprobe_regs.S | 62 ++++++++++++
> > arch/powerpc/lib/test_kprobes.c | 115 ++++++++++++++++++++++
> > include/linux/kprobes.h | 11 +++
> > kernel/test_kprobes.c | 183 ++++++++++++++++++++++++++++++++++++
> > 6 files changed, 377 insertions(+), 1 deletion(-)
> > create mode 100644 arch/powerpc/lib/test_kprobe_regs.S
> > create mode 100644 arch/powerpc/lib/test_kprobes.c
> >
> > diff --git a/arch/powerpc/include/asm/kprobes.h b/arch/powerpc/include/asm/kprobes.h
> > index 566da372e02b..10c91d3132a1 100644
> > --- a/arch/powerpc/include/asm/kprobes.h
> > +++ b/arch/powerpc/include/asm/kprobes.h
> > @@ -124,6 +124,10 @@ static inline int skip_singlestep(struct kprobe *p, struct pt_regs *regs,
> > return 0;
> > }
> > #endif
> > +#if defined(CONFIG_KPROBES_SANITY_TEST) && defined(CONFIG_PPC64)
> > +#define HAVE_KPROBES_REGS_SANITY_TEST
> > +void arch_kprobe_regs_set_ptregs(struct pt_regs *regs);
> > +#endif
> > #else
> > static inline int kprobe_handler(struct pt_regs *regs) { return 0; }
> > static inline int kprobe_post_handler(struct pt_regs *regs) { return 0; }
> > diff --git a/arch/powerpc/lib/Makefile b/arch/powerpc/lib/Makefile
> > index 3c3146ba62da..8a0bb8e20179 100644
> > --- a/arch/powerpc/lib/Makefile
> > +++ b/arch/powerpc/lib/Makefile
> > @@ -27,7 +27,8 @@ obj64-y += copypage_64.o copyuser_64.o mem_64.o hweight_64.o \
> >
> > obj64-$(CONFIG_SMP) += locks.o
> > obj64-$(CONFIG_ALTIVEC) += vmx-helper.o
> > -obj64-$(CONFIG_KPROBES_SANITY_TEST) += test_emulate_step.o
> > +obj64-$(CONFIG_KPROBES_SANITY_TEST) += test_emulate_step.o test_kprobe_regs.o \
> > + test_kprobes.o
> >
> > obj-y += checksum_$(BITS).o checksum_wrappers.o
> >
> > diff --git a/arch/powerpc/lib/test_kprobe_regs.S b/arch/powerpc/lib/test_kprobe_regs.S
> > new file mode 100644
> > index 000000000000..4e95eca6dcd3
> > --- /dev/null
> > +++ b/arch/powerpc/lib/test_kprobe_regs.S
> > @@ -0,0 +1,62 @@
> > +/*
> > + * test_kprobe_regs: architectural helpers for validating pt_regs
> > + * received on a kprobe.
> > + *
> > + * Copyright 2017 Naveen N. Rao <naveen.n.rao@xxxxxxxxxxxxxxxxxx>
> > + * IBM Corporation
> > + *
> > + * This program is free software; you can redistribute it and/or
> > + * modify it under the terms of the GNU General Public License
> > + * as published by the Free Software Foundation; version 2
> > + * of the License.
> > + */
> > +
> > +#include <asm/ppc_asm.h>
> > +#include <asm/asm-offsets.h>
> > +#include <asm/ptrace.h>
> > +
> > +_GLOBAL(arch_kprobe_regs_function)
> > + mflr r0
> > + std r0, LRSAVE(r1)
> > + stdu r1, -SWITCH_FRAME_SIZE(r1)
> > +
> > + /* Tell pre handler about our pt_regs location */
> > + addi r3, r1, STACK_FRAME_OVERHEAD
> > + bl arch_kprobe_regs_set_ptregs
> > +
> > + /* Load back our true LR */
> > + ld r0, (SWITCH_FRAME_SIZE + LRSAVE)(r1)
> > + mtlr r0
> > +
> > + /* Save all SPRs that we care about */
> > + mfctr r0
> > + std r0, _CTR(r1)
> > + mflr r0
> > + std r0, _LINK(r1)
> > + mfspr r0, SPRN_XER
> > + std r0, _XER(r1)
> > + mfcr r0
> > + std r0, _CCR(r1)
> > +
> > + /* Now, save all GPRs */
> > + SAVE_2GPRS(0, r1)
> > + SAVE_10GPRS(2, r1)
> > + SAVE_10GPRS(12, r1)
> > + SAVE_10GPRS(22, r1)
> > +
> > + /* We're now ready to be probed */
> > +.global arch_kprobe_regs_probepoint
> > +arch_kprobe_regs_probepoint:
> > + nop
> > +
> > +#ifdef CONFIG_KPROBES_ON_FTRACE
> > + /* Let's also test KPROBES_ON_FTRACE */
> > + bl kprobe_regs_kp_on_ftrace_target
> > + nop
> > +#endif
> > +
> > + /* All done */
> > + addi r1, r1, SWITCH_FRAME_SIZE
> > + ld r0, LRSAVE(r1)
> > + mtlr r0
> > + blr
> > diff --git a/arch/powerpc/lib/test_kprobes.c b/arch/powerpc/lib/test_kprobes.c
> > new file mode 100644
> > index 000000000000..23f7a7ffcdd6
> > --- /dev/null
> > +++ b/arch/powerpc/lib/test_kprobes.c
> > @@ -0,0 +1,115 @@
> > +/*
> > + * test_kprobes: architectural helpers for validating pt_regs
> > + * received on a kprobe.
> > + *
> > + * Copyright 2017 Naveen N. Rao <naveen.n.rao@xxxxxxxxxxxxxxxxxx>
> > + * IBM Corporation
> > + *
> > + * This program is free software; you can redistribute it and/or
> > + * modify it under the terms of the GNU General Public License
> > + * as published by the Free Software Foundation; version 2
> > + * of the License.
> > + */
> > +
> > +#define pr_fmt(fmt) "Kprobe smoke test (regs): " fmt
> > +
> > +#include <asm/ptrace.h>
> > +#include <linux/kernel.h>
> > +#include <linux/kprobes.h>
> > +
> > +static struct pt_regs *r;
> > +
> > +void arch_kprobe_regs_set_ptregs(struct pt_regs *regs)
> > +{
> > + r = regs;
> > +}
> > +
> > +static int validate_regs(struct kprobe *p, struct pt_regs *regs,
> > + int kp_on_ftrace, int post_handler)
> > +{
> > + int i, ret = 1;
> > +
> > + if (!r) {
> > + pr_err("pt_regs not setup!\n");
> > + return 0;
> > + }
> > +
> > + if (regs->gpr[1] + STACK_FRAME_OVERHEAD != (unsigned long)r) {
> > + /* We'll continue since this may just indicate an incorrect r1 */
> > + pr_err("pt_regs pointer/r1 doesn't point where we expect!\n");
> > + ret = 0;
> > + }
> > +
> > + for (i = 0; i < 32; i++) {
> > + /* KPROBES_ON_FTRACE may have stomped r0 in the prologue */
> > + if (r->gpr[i] != regs->gpr[i] && (!kp_on_ftrace || i != 0)) {
> > + pr_err("gpr[%d] expected: 0x%lx, received: 0x%lx\n",
> > + i, r->gpr[i], regs->gpr[i]);
> > + ret = 0;
> > + }
> > + }

Hmm, is this check really needed? See below(*)

> > +
> > + if (r->ctr != regs->ctr) {
> > + pr_err("ctr expected: 0x%lx, received: 0x%lx\n",
> > + r->ctr, regs->ctr);
> > + ret = 0;
> > + }
> > +
> > + if (r->link != regs->link && !kp_on_ftrace) {
> > + pr_err("link expected: 0x%lx, received: 0x%lx\n",
> > + r->link, regs->link);
> > + ret = 0;
> > + }
> > +
> > + /* KPROBES_ON_FTRACE *must* have clobbered link */
> > + if (r->link == regs->link && kp_on_ftrace) {
> > + pr_err("link register not clobbered for KPROBES_ON_FTRACE!\n");
> > + ret = 0;
> > + }
> > +
> > + if (r->xer != regs->xer) {
> > + pr_err("xer expected: 0x%lx, received: 0x%lx\n",
> > + r->xer, regs->xer);
> > + ret = 0;
> > + }
> > +
> > + if (r->ccr != regs->ccr) {
> > + pr_err("ccr expected: 0x%lx, received: 0x%lx\n",
> > + r->ccr, regs->ccr);
> > + ret = 0;
> > + }
> > +
> > + if (!post_handler && regs->nip != (unsigned long)p->addr) {
> > + pr_err("nip expected: 0x%lx, received: 0x%lx\n",
> > + (unsigned long)p->addr, regs->nip);
> > + ret = 0;
> > + }
> > +
> > + if (post_handler &&
> > + regs->nip != (unsigned long)p->addr + sizeof(kprobe_opcode_t)) {
> > + pr_err("post_handler: nip expected: 0x%lx, received: 0x%lx\n",
> > + (unsigned long)p->addr + sizeof(kprobe_opcode_t),
> > + regs->nip);
> > + ret = 0;
> > + }
> > +
> > + return ret;
> > +}
> > +
> > +int arch_kprobe_regs_pre_handler(struct kprobe *p, struct pt_regs *regs)
> > +{
> > + return validate_regs(p, regs, 0, 0);
> > +}
> > +
> > +int arch_kprobe_regs_post_handler(struct kprobe *p, struct pt_regs *regs,
> > + unsigned long flags)
> > +{
> > + return validate_regs(p, regs, 0, 1);
> > +}
> > +
> > +#ifdef CONFIG_KPROBES_ON_FTRACE
> > +int arch_kp_on_ftrace_pre_handler(struct kprobe *p, struct pt_regs *regs)
> > +{
> > + return validate_regs(p, regs, 1, 0);
> > +}
> > +#endif
> > diff --git a/include/linux/kprobes.h b/include/linux/kprobes.h
> > index 541df0b5b815..adfbb5b27acd 100644
> > --- a/include/linux/kprobes.h
> > +++ b/include/linux/kprobes.h
> > @@ -253,6 +253,17 @@ static inline void kretprobe_assert(struct kretprobe_instance *ri,
> >
> > #ifdef CONFIG_KPROBES_SANITY_TEST
> > extern int init_test_probes(void);
> > +#ifdef HAVE_KPROBES_REGS_SANITY_TEST
> > +extern void arch_kprobe_regs_function(void);
> > +extern void arch_kprobe_regs_probepoint(void);
> > +extern int arch_kprobe_regs_pre_handler(struct kprobe *p, struct pt_regs *regs);
> > +extern int arch_kprobe_regs_post_handler(struct kprobe *p, struct pt_regs *regs,
> > + unsigned long flags);
> > +#ifdef CONFIG_KPROBES_ON_FTRACE
> > +extern void kprobe_regs_kp_on_ftrace_target(void);
> > +extern int arch_kp_on_ftrace_pre_handler(struct kprobe *p, struct pt_regs *regs);
> > +#endif
> > +#endif
> > #else
> > static inline int init_test_probes(void)
> > {
> > diff --git a/kernel/test_kprobes.c b/kernel/test_kprobes.c
> > index 0dbab6d1acb4..92011726cc69 100644
> > --- a/kernel/test_kprobes.c
> > +++ b/kernel/test_kprobes.c
> > @@ -19,6 +19,7 @@
> > #include <linux/kernel.h>
> > #include <linux/kprobes.h>
> > #include <linux/random.h>
> > +#include <linux/workqueue.h>
> >
> > #define div_factor 3
> >
> > @@ -334,6 +335,166 @@ static int test_kretprobes(void)
> > }
> > #endif /* CONFIG_KRETPROBES */
> >
> > +#ifdef HAVE_KPROBES_REGS_SANITY_TEST
> > +static int kprobe_regs_pre_handler(struct kprobe *p, struct pt_regs *regs)
> > +{
> > + /* architectural helper returns 0 if validation fails */
> > + preh_val = arch_kprobe_regs_pre_handler(p, regs);
> > + return 0;
> > +}
> > +
> > +static void kprobe_regs_post_handler(struct kprobe *p, struct pt_regs *regs,
> > + unsigned long flags)
> > +{
> > + posth_val = arch_kprobe_regs_post_handler(p, regs, flags);
> > +}
> > +
> > +static struct kprobe kpr = {
> > + .symbol_name = "arch_kprobe_regs_probepoint",
> > + .pre_handler = kprobe_regs_pre_handler,
> > + .post_handler = kprobe_regs_post_handler,
> > +};
> > +

> > +static int test_kprobe_regs(void)
> > +{
> > + int ret;
> > + kprobe_opcode_t *addr;
> > +
> > + preh_val = 0;
> > + posth_val = 0;
> > +
> > + ret = register_kprobe(&kpr);
> > + if (ret < 0) {
> > + pr_err("register_kprobe returned %d\n", ret);
> > + return ret;
> > + }
> > +
> > + /* Let's see if this probe was optimized */
> > + addr = kprobe_lookup_name(kpr.symbol_name, 0);

What happen if addr == NULL?
Since this already done in register_kprobe, you'd better use
kpr.addr.

> > + if (addr && *addr != BREAKPOINT_INSTRUCTION) {
> > + pr_err("kprobe with post_handler optimized\n");

Hmm, this message is not appropriate if the arch doesn't support
optprobe. Moreover, using BREAKPOINT_INSTRUCTION or not depends
on each arch. So, I suggest this as;

if (kprobe_optimized(&kpr)) {
pr_err("kprobe with post_handler optimized\n");
goto error;

And if you would like to check the instruction, please use
probe_kernel_read(), and introduce arch-depend helper as
below;

} else if (arch_kprobe_validate_insn(&kpr)) {
pr_err("kprobe breakpoint is not armed\n");
goto error;
}

Where (typical case, like ppc),

int arch_kprobe_validate_insn(struct kprobe *kp)
{
kprobe_opcode_t buf;
int ret;

ret = probe_kernel_read(&buf, kp->addr, sizeof(buf));
if (ret)
return ret;
if (buf != BREAKPOINT_INSTRUCTION)
return -EINVAL;
return 0;
}

> > + unregister_kprobe(&kpr);
> > + return -1;
> > + }
> > +
> > + arch_kprobe_regs_function();
> > + unregister_kprobe(&kpr);
> > +
> > + if (preh_val == 0) {
> > + pr_err("kprobe pre_handler regs validation failed\n");
> > + handler_errors++;
> > + }
> > +
> > + if (posth_val == 0) {
> > + pr_err("kprobe post_handler not called\n");
> > + handler_errors++;
> > + }
> > +
> > + return 0;
> > +}
> > +

> > +#ifdef CONFIG_KPROBES_ON_FTRACE
> > +void kprobe_regs_kp_on_ftrace_target(void)
> > +{
> > + posth_val = preh_val + div_factor;
> > +}
> > +
> > +static int kp_on_ftrace_pre_handler(struct kprobe *p, struct pt_regs *regs)
> > +{
> > + /* architectural helper returns 0 if validation fails */
> > + preh_val = arch_kp_on_ftrace_pre_handler(p, regs);

Here, I think you'd better to call arch_kprobe_regs_pre_handler(p, regs);
so that user can sure the handler's behavior has no difference.

(*) If you would like to check the kprobe_on_ftrace arch inplementation,
it should be a separated function, like

arch_validate_kprobe_on_ftrace(p, regs);

> > + return 0;
> > +}
> > +
> > +static struct kprobe kprf = {
> > + .symbol_name = "kprobe_regs_kp_on_ftrace_target",
> > + .pre_handler = kp_on_ftrace_pre_handler,

Also, we'd better add post_handler here so that it is able to check
compatibilty.

> > +};
> > +
> > +static int test_kp_on_ftrace_regs(void)
> > +{
> > + int ret;
> > +
> > + preh_val = 0;
> > +
> > + ret = register_kprobe(&kprf);
> > + if (ret < 0) {
> > + pr_err("register_kprobe returned %d\n", ret);
> > + return ret;
> > + }
> > +
> > + arch_kprobe_regs_function();
> > + unregister_kprobe(&kprf);
> > +
> > + if (preh_val == 0) {
> > + pr_err("kp_on_ftrace pre_handler regs validation failed\n");
> > + handler_errors++;
> > + }
> > +
> > + return 0;
> > +}
> > +#endif
> > +
> > +#ifdef CONFIG_OPTPROBES
> > +static void test_optprobe_regs(struct work_struct *work);
> > +static DECLARE_DELAYED_WORK(test_optprobe_regs_work, test_optprobe_regs);
> > +int kprobe_registered;
> > +
> > +static struct kprobe kpor = {
> > + .symbol_name = "arch_kprobe_regs_probepoint",
> > + .pre_handler = kprobe_regs_pre_handler,
> > +};
> > +
> > +static void test_optprobe_regs_setup(void)
> > +{
> > + int ret;
> > +
> > + ret = register_kprobe(&kpor);
> > + if (ret < 0) {
> > + pr_err("register_kprobe returned %d\n", ret);
> > + return;
> > + }
> > +
> > + kprobe_registered = 1;
> > +}
> > +
> > +static void test_optprobe_regs(struct work_struct *work)
> > +{
> > + kprobe_opcode_t *addr;
> > +
> > + if (!kprobe_registered) {
> > + errors++;
> > + goto summary;
> > + }
> > +
> > + /* Let's see if this probe was optimized */
> > + addr = kprobe_lookup_name(kpor.symbol_name, 0);
> > + if (addr && *addr == BREAKPOINT_INSTRUCTION) {

Here, same as above, we need arch_optprobe_validate_insn(kp).

Thank you,

--
Masami Hiramatsu <mhiramat@xxxxxxxxxx>

Next message: Schöfegger Stefan: "Re: [PATCH v2 1/1] PCI: imx6: Add pcie compliance test option"
Previous message: Tony Lindgren: "Re: [PATCHv2] ARM: OMAP: PM: stop early on systems without twl"
In reply to: Masami Hiramatsu: "Re: [PATCH] kernel/kprobes: Add test to validate pt_regs"
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