Re: [PATCH v13 08/10] arm64: Add trampoline code for kretprobes

[Masami Hiramatsu <mhiramat@kernel.org>]

On Thu,  2 Jun 2016 23:26:22 -0400
David Long <dave.long@linaro.org> wrote:

> 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.

OK, I think we had discussed why this was not included to the next patch.
(Not like to merge patches from different person?)

Acked-by: Masami Hiramatsu <mhiramat@kernel.org>

Thanks,


> 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 | 85 ++++++++++++++++++++++++++++++++++
>  5 files changed, 104 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 46724a1..75751b7 100644
> --- a/arch/arm64/kernel/Makefile
> +++ b/arch/arm64/kernel/Makefile
> @@ -38,6 +38,7 @@ 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 f8e5d47..03dfa27 100644
> --- a/arch/arm64/kernel/asm-offsets.c
> +++ b/arch/arm64/kernel/asm-offsets.c
> @@ -51,6 +51,17 @@ 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 9d0ad47..b35f76f 100644
> --- a/arch/arm64/kernel/kprobes.c
> +++ b/arch/arm64/kernel/kprobes.c
> @@ -575,6 +575,11 @@ bool arch_within_kprobe_blacklist(unsigned long addr)
>  	return false;
>  }
>  
> +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..ba37d85
> --- /dev/null
> +++ b/arch/arm64/kernel/kprobes_trampoline.S
> @@ -0,0 +1,85 @@
> +/*
> + * 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
> +	stp x0, x1, [sp, #S_X0]
> +	stp x2, x3, [sp, #S_X2]
> +	stp x4, x5, [sp, #S_X4]
> +	stp x6, x7, [sp, #S_X6]
> +	stp x8, x9, [sp, #S_X8]
> +	stp x10, x11, [sp, #S_X10]
> +	stp x12, x13, [sp, #S_X12]
> +	stp x14, x15, [sp, #S_X14]
> +	stp x16, x17, [sp, #S_X16]
> +	stp x18, x19, [sp, #S_X18]
> +	stp x20, x21, [sp, #S_X20]
> +	stp x22, x23, [sp, #S_X22]
> +	stp x24, x25, [sp, #S_X24]
> +	stp x26, x27, [sp, #S_X26]
> +	stp x28, x29, [sp, #S_X28]
> +	add x0, sp, #S_FRAME_SIZE
> +	stp lr, x0, [sp, #S_LR]
> +/*
> + * Construct a useful saved PSTATE
> + */
> +	mrs x0, nzcv
> +	and x0, x0, #(PSR_N_BIT | PSR_Z_BIT | PSR_C_BIT | PSR_V_BIT)
> +	mrs x1, daif
> +	and x1, x1, #(PSR_D_BIT | PSR_A_BIT | PSR_I_BIT | PSR_F_BIT)
> +	orr x0, x0, x1
> +	mrs x1, CurrentEL
> +	and x1, x1, #(3 << 2)
> +	orr x0, x1, x0
> +	mrs x1, SPSel
> +	and x1, x1, #1
> +	orr x0, x1, x0
> +	str x0, [sp, #S_PSTATE]
> +.endm
> +
> +.macro restore_all_base_regs
> +	ldr x0, [sp, #S_PSTATE]
> +	and x0, x0, #(PSR_N_BIT | PSR_Z_BIT | PSR_C_BIT | PSR_V_BIT)
> +	msr nzcv, x0
> +	ldp x0, x1, [sp, #S_X0]
> +	ldp x2, x3, [sp, #S_X2]
> +	ldp x4, x5, [sp, #S_X4]
> +	ldp x6, x7, [sp, #S_X6]
> +	ldp x8, x9, [sp, #S_X8]
> +	ldp x10, x11, [sp, #S_X10]
> +	ldp x12, x13, [sp, #S_X12]
> +	ldp x14, x15, [sp, #S_X14]
> +	ldp x16, x17, [sp, #S_X16]
> +	ldp x18, x19, [sp, #S_X18]
> +	ldp x20, x21, [sp, #S_X20]
> +	ldp x22, x23, [sp, #S_X22]
> +	ldp x24, x25, [sp, #S_X24]
> +	ldp x26, x27, [sp, #S_X26]
> +	ldp x28, x29, [sp, #S_X28]
> +.endm
> +
> +ENTRY(kretprobe_trampoline)
> +
> +	sub sp, sp, #S_FRAME_SIZE
> +
> +	save_all_base_regs
> +
> +	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
> +
> +	add sp, sp, #S_FRAME_SIZE
> +
> +	ret
> +
> +ENDPROC(kretprobe_trampoline)
> -- 
> 2.5.0
> 


-- 
Masami Hiramatsu <mhiramat@kernel.org>