Messages in this thread | | | Subject | Re: [PATCH v15 08/10] arm64: Add trampoline code for kretprobes | From | David Long <> | Date | Wed, 20 Jul 2016 14:28:39 -0400 |
| |
On 07/19/2016 09:46 AM, Catalin Marinas wrote: > On Fri, Jul 08, 2016 at 12:35:52PM -0400, David Long wrote: >> --- /dev/null >> +++ b/arch/arm64/kernel/probes/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) > > I don't think you need the masking here, the mrs should return the > corresponding 4 bits. >
OK. I see you've done that.
>> + orr x0, x0, x1 >> + mrs x1, CurrentEL >> + and x1, x1, #(3 << 2) >> + orr x0, x1, x0 >> + mrs x1, SPSel >> + and x1, x1, #1 > > Same here.
OK. ^
> >> + orr x0, x1, x0 >> + str x0, [sp, #S_PSTATE] >> +.endm > > How is this pstate used, other than the restoring of the condition flag > in the restore_all_base_regs macro? Does a kretprobes handler need > access to them? >
A kretprobes handler should probably be able to examine a reasonable pstate value, particularly in terms of DAIF. As I recall not having a valid DAIF was an issue at one time.
> Anyway, it's worth doing an stp xzr, x0, [sp, S_PC] so that we > initialise the pc in pt_regs. >
OK. Looks like you've done this.
>> + >> +.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) >
Thanks, -dl
| |