On Tue, Nov 26, 2019 at 04:21:38PM +1100, Jordan Niethe wrote:
> Uprobes can execute instructions out of line. Increase the size of the
> buffer used for this so that this works for prefixed instructions. Take
> into account the length of prefixed instructions when fixing up the nip.
>
> Signed-off-by: Jordan Niethe <jniet...@gmail.com>
> ---
> arch/powerpc/include/asm/uprobes.h | 18 ++++++++++++++----
> arch/powerpc/kernel/uprobes.c | 4 ++--
> 2 files changed, 16 insertions(+), 6 deletions(-)
>
> diff --git a/arch/powerpc/include/asm/uprobes.h
> b/arch/powerpc/include/asm/uprobes.h
> index 2bbdf27d09b5..5b5e8a3d2f55 100644
> --- a/arch/powerpc/include/asm/uprobes.h
> +++ b/arch/powerpc/include/asm/uprobes.h
> @@ -14,18 +14,28 @@
>
> typedef ppc_opcode_t uprobe_opcode_t;
>
> +/*
> + * We have to ensure we have enought space for prefixed instructions, which
minor typo of `enought` and we can have something like below,
s/We have to ensure we have enought/Ensure we have enough
-- Bala
> + * are double the size of a word instruction, i.e. 8 bytes. However,
> + * sometimes it is simpler to treat a prefixed instruction like 2 word
> + * instructions.
> + */
> #define MAX_UINSN_BYTES 4
> -#define UPROBE_XOL_SLOT_BYTES (MAX_UINSN_BYTES)
> +#define UPROBE_XOL_SLOT_BYTES (2 * MAX_UINSN_BYTES)
>
> /* The following alias is needed for reference from arch-agnostic code */
> #define UPROBE_SWBP_INSN BREAKPOINT_INSTRUCTION
> #define UPROBE_SWBP_INSN_SIZE 4 /* swbp insn size in bytes */
>
> struct arch_uprobe {
> + /*
> + * Ensure there is enough space for prefixed instructions. Prefixed
> + * instructions must not cross 64-byte boundaries.
> + */
> union {
> - u32 insn;
> - u32 ixol;
> - };
> + uprobe_opcode_t insn[2];
> + uprobe_opcode_t ixol[2];
> + } __aligned(64);
> };
>
> struct arch_uprobe_task {
> diff --git a/arch/powerpc/kernel/uprobes.c b/arch/powerpc/kernel/uprobes.c
> index ab1077dc6148..cfcea6946f8b 100644
> --- a/arch/powerpc/kernel/uprobes.c
> +++ b/arch/powerpc/kernel/uprobes.c
> @@ -111,7 +111,7 @@ int arch_uprobe_post_xol(struct arch_uprobe *auprobe,
> struct pt_regs *regs)
> * support doesn't exist and have to fix-up the next instruction
> * to be executed.
> */
> - regs->nip = utask->vaddr + MAX_UINSN_BYTES;
> + regs->nip = utask->vaddr + ((IS_PREFIX(auprobe->insn[0])) ? 8 : 4);
>
> user_disable_single_step(current);
> return 0;
> @@ -173,7 +173,7 @@ bool arch_uprobe_skip_sstep(struct arch_uprobe *auprobe,
> struct pt_regs *regs)
> * emulate_step() returns 1 if the insn was successfully emulated.
> * For all other cases, we need to single-step in hardware.
> */
> - ret = emulate_step(regs, auprobe->insn, 0);
> + ret = emulate_step(regs, auprobe->insn[0], auprobe->insn[1]);
> if (ret > 0)
> return true;
>
> --
> 2.20.1
>
