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    Subject[PATCH v7 3.2-rc2 17/30] x86: arch specific hooks for pre/post singlestep handling.

    Hooks for handling pre singlestepping and post singlestepping.

    Signed-off-by: Jim Keniston <jkenisto@us.ibm.com>
    Signed-off-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
    ---
    arch/x86/include/asm/uprobes.h | 2 +
    arch/x86/kernel/uprobes.c | 135 ++++++++++++++++++++++++++++++++++++++++
    2 files changed, 137 insertions(+), 0 deletions(-)

    diff --git a/arch/x86/include/asm/uprobes.h b/arch/x86/include/asm/uprobes.h
    index cf794bf..99d7d4b 100644
    --- a/arch/x86/include/asm/uprobes.h
    +++ b/arch/x86/include/asm/uprobes.h
    @@ -47,6 +47,8 @@ struct uprobe_task_arch_info {};
    struct uprobe;
    extern int analyze_insn(struct mm_struct *mm, struct uprobe *uprobe);
    extern void set_instruction_pointer(struct pt_regs *regs, unsigned long vaddr);
    +extern int pre_xol(struct uprobe *uprobe, struct pt_regs *regs);
    +extern int post_xol(struct uprobe *uprobe, struct pt_regs *regs);
    extern int uprobe_exception_notify(struct notifier_block *self,
    unsigned long val, void *data);
    #endif /* _ASM_UPROBES_H */
    diff --git a/arch/x86/kernel/uprobes.c b/arch/x86/kernel/uprobes.c
    index 2ee5ddc..0792fc8 100644
    --- a/arch/x86/kernel/uprobes.c
    +++ b/arch/x86/kernel/uprobes.c
    @@ -25,6 +25,7 @@
    #include <linux/sched.h>
    #include <linux/ptrace.h>
    #include <linux/uprobes.h>
    +#include <linux/uaccess.h>

    #include <linux/kdebug.h>
    #include <asm/insn.h>
    @@ -409,6 +410,140 @@ void set_instruction_pointer(struct pt_regs *regs, unsigned long vaddr)
    }

    /*
    + * pre_xol - prepare to execute out of line.
    + * @uprobe: the probepoint information.
    + * @regs: reflects the saved user state of @tsk.
    + *
    + * If we're emulating a rip-relative instruction, save the contents
    + * of the scratch register and store the target address in that register.
    + *
    + * Returns true if @uprobe->opcode is @bkpt_insn.
    + */
    +#ifdef CONFIG_X86_64
    +int pre_xol(struct uprobe *uprobe, struct pt_regs *regs)
    +{
    + struct uprobe_task_arch_info *tskinfo = &current->utask->tskinfo;
    +
    + regs->ip = current->utask->xol_vaddr;
    + if (uprobe->fixups & UPROBES_FIX_RIP_AX) {
    + tskinfo->saved_scratch_register = regs->ax;
    + regs->ax = current->utask->vaddr;
    + regs->ax += uprobe->arch_info.rip_rela_target_address;
    + } else if (uprobe->fixups & UPROBES_FIX_RIP_CX) {
    + tskinfo->saved_scratch_register = regs->cx;
    + regs->cx = current->utask->vaddr;
    + regs->cx += uprobe->arch_info.rip_rela_target_address;
    + }
    + return 0;
    +}
    +#else
    +int pre_xol(struct uprobe *uprobe, struct pt_regs *regs)
    +{
    + regs->ip = current->utask->xol_vaddr;
    + return 0;
    +}
    +#endif
    +
    +/*
    + * Called by post_xol() to adjust the return address pushed by a call
    + * instruction executed out of line.
    + */
    +static int adjust_ret_addr(unsigned long sp, long correction)
    +{
    + int rasize, ncopied;
    + long ra = 0;
    +
    + if (is_32bit_app(current))
    + rasize = 4;
    + else
    + rasize = 8;
    +
    + ncopied = copy_from_user(&ra, (void __user *)sp, rasize);
    + if (unlikely(ncopied))
    + return -EFAULT;
    +
    + ra += correction;
    + ncopied = copy_to_user((void __user *)sp, &ra, rasize);
    + if (unlikely(ncopied))
    + return -EFAULT;
    +
    + return 0;
    +}
    +
    +#ifdef CONFIG_X86_64
    +static bool is_riprel_insn(struct uprobe *uprobe)
    +{
    + return ((uprobe->fixups &
    + (UPROBES_FIX_RIP_AX | UPROBES_FIX_RIP_CX)) != 0);
    +}
    +
    +static void handle_riprel_post_xol(struct uprobe *uprobe,
    + struct pt_regs *regs, long *correction)
    +{
    + if (is_riprel_insn(uprobe)) {
    + struct uprobe_task_arch_info *tskinfo;
    + tskinfo = &current->utask->tskinfo;
    +
    + if (uprobe->fixups & UPROBES_FIX_RIP_AX)
    + regs->ax = tskinfo->saved_scratch_register;
    + else
    + regs->cx = tskinfo->saved_scratch_register;
    + /*
    + * The original instruction includes a displacement, and so
    + * is 4 bytes longer than what we've just single-stepped.
    + * Fall through to handle stuff like "jmpq *...(%rip)" and
    + * "callq *...(%rip)".
    + */
    + *correction += 4;
    + }
    +}
    +#else
    +static void handle_riprel_post_xol(struct uprobe *uprobe,
    + struct pt_regs *regs, long *correction)
    +{
    +}
    +#endif
    +
    +/*
    + * Called after single-stepping. To avoid the SMP problems that can
    + * occur when we temporarily put back the original opcode to
    + * single-step, we single-stepped a copy of the instruction.
    + *
    + * This function prepares to resume execution after the single-step.
    + * We have to fix things up as follows:
    + *
    + * Typically, the new ip is relative to the copied instruction. We need
    + * to make it relative to the original instruction (FIX_IP). Exceptions
    + * are return instructions and absolute or indirect jump or call instructions.
    + *
    + * If the single-stepped instruction was a call, the return address that
    + * is atop the stack is the address following the copied instruction. We
    + * need to make it the address following the original instruction (FIX_CALL).
    + *
    + * If the original instruction was a rip-relative instruction such as
    + * "movl %edx,0xnnnn(%rip)", we have instead executed an equivalent
    + * instruction using a scratch register -- e.g., "movl %edx,(%rax)".
    + * We need to restore the contents of the scratch register and adjust
    + * the ip, keeping in mind that the instruction we executed is 4 bytes
    + * shorter than the original instruction (since we squeezed out the offset
    + * field). (FIX_RIP_AX or FIX_RIP_CX)
    + */
    +int post_xol(struct uprobe *uprobe, struct pt_regs *regs)
    +{
    + struct uprobe_task *utask = current->utask;
    + int result = 0;
    + long correction;
    +
    + correction = (long)(utask->vaddr - utask->xol_vaddr);
    + handle_riprel_post_xol(uprobe, regs, &correction);
    + if (uprobe->fixups & UPROBES_FIX_IP)
    + regs->ip += correction;
    + if (uprobe->fixups & UPROBES_FIX_CALL)
    + result = adjust_ret_addr(regs->sp, correction);
    + return result;
    +}
    +
    +/*
    * Wrapper routine for handling exceptions.
    */
    int uprobe_exception_notify(struct notifier_block *self,


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