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    Subject[RFC PATCH 3/6] rethook: x86: Add rethook x86 implementation
    Date
    Add rethook for x86 implementation. Most of the code
    has been copied from kretprobes on x86.

    Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
    ---
    arch/x86/Kconfig | 1
    arch/x86/kernel/Makefile | 1
    arch/x86/kernel/rethook.c | 115 +++++++++++++++++++++++++++++++++++++++++++++
    3 files changed, 117 insertions(+)
    create mode 100644 arch/x86/kernel/rethook.c

    diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
    index 7399327d1eff..939c4c897e63 100644
    --- a/arch/x86/Kconfig
    +++ b/arch/x86/Kconfig
    @@ -219,6 +219,7 @@ config X86
    select HAVE_KPROBES_ON_FTRACE
    select HAVE_FUNCTION_ERROR_INJECTION
    select HAVE_KRETPROBES
    + select HAVE_RETHOOK
    select HAVE_KVM
    select HAVE_LIVEPATCH if X86_64
    select HAVE_MIXED_BREAKPOINTS_REGS
    diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
    index 2ff3e600f426..66593d8c4d74 100644
    --- a/arch/x86/kernel/Makefile
    +++ b/arch/x86/kernel/Makefile
    @@ -106,6 +106,7 @@ obj-$(CONFIG_FUNCTION_GRAPH_TRACER) += ftrace.o
    obj-$(CONFIG_FTRACE_SYSCALLS) += ftrace.o
    obj-$(CONFIG_X86_TSC) += trace_clock.o
    obj-$(CONFIG_TRACING) += trace.o
    +obj-$(CONFIG_RETHOOK) += rethook.o
    obj-$(CONFIG_CRASH_CORE) += crash_core_$(BITS).o
    obj-$(CONFIG_KEXEC_CORE) += machine_kexec_$(BITS).o
    obj-$(CONFIG_KEXEC_CORE) += relocate_kernel_$(BITS).o crash.o
    diff --git a/arch/x86/kernel/rethook.c b/arch/x86/kernel/rethook.c
    new file mode 100644
    index 000000000000..f2f3b9526e43
    --- /dev/null
    +++ b/arch/x86/kernel/rethook.c
    @@ -0,0 +1,115 @@
    +// SPDX-License-Identifier: GPL-2.0-or-later
    +/*
    + * x86 implementation of rethook. Mostly copied from arch/x86/kernel/kprobes/core.c.
    + */
    +#include <linux/bug.h>
    +#include <linux/rethook.h>
    +#include <linux/kprobes.h>
    +
    +#include "kprobes/common.h"
    +
    +/*
    + * Called from arch_rethook_trampoline
    + */
    +__used __visible void arch_rethook_trampoline_callback(struct pt_regs *regs)
    +{
    + unsigned long *frame_pointer;
    +
    + /* fixup registers */
    + regs->cs = __KERNEL_CS;
    +#ifdef CONFIG_X86_32
    + regs->gs = 0;
    +#endif
    + regs->ip = (unsigned long)&arch_rethook_trampoline;
    + regs->orig_ax = ~0UL;
    + regs->sp += sizeof(long);
    + frame_pointer = &regs->sp + 1;
    +
    + /*
    + * The return address at 'frame_pointer' is recovered by the
    + * arch_rethook_fixup_return() which called from this
    + * rethook_trampoline_handler().
    + */
    + rethook_trampoline_handler(regs, (unsigned long)frame_pointer);
    +
    + /*
    + * Copy FLAGS to 'pt_regs::sp' so that arch_rethook_trapmoline()
    + * can do RET right after POPF.
    + */
    + regs->sp = regs->flags;
    +}
    +NOKPROBE_SYMBOL(arch_rethook_trampoline_callback);
    +
    +/*
    + * When a target function returns, this code saves registers and calls
    + * arch_rethook_trampoline_callback(), which calls the rethook handler.
    + */
    +asm(
    + ".text\n"
    + ".global arch_rethook_trampoline\n"
    + ".type arch_rethook_trampoline, @function\n"
    + "arch_rethook_trampoline:\n"
    +#ifdef CONFIG_X86_64
    + /* Push a fake return address to tell the unwinder it's a kretprobe. */
    + " pushq $arch_rethook_trampoline\n"
    + UNWIND_HINT_FUNC
    + /* Save the 'sp - 8', this will be fixed later. */
    + " pushq %rsp\n"
    + " pushfq\n"
    + SAVE_REGS_STRING
    + " movq %rsp, %rdi\n"
    + " call arch_rethook_trampoline_callback\n"
    + RESTORE_REGS_STRING
    + /* In the callback function, 'regs->flags' is copied to 'regs->sp'. */
    + " addq $8, %rsp\n"
    + " popfq\n"
    +#else
    + /* Push a fake return address to tell the unwinder it's a kretprobe. */
    + " pushl $arch_rethook_trampoline\n"
    + UNWIND_HINT_FUNC
    + /* Save the 'sp - 4', this will be fixed later. */
    + " pushl %esp\n"
    + " pushfl\n"
    + SAVE_REGS_STRING
    + " movl %esp, %eax\n"
    + " call arch_rethook_trampoline_callback\n"
    + RESTORE_REGS_STRING
    + /* In the callback function, 'regs->flags' is copied to 'regs->sp'. */
    + " addl $4, %esp\n"
    + " popfl\n"
    +#endif
    + " ret\n"
    + ".size arch_rethook_trampoline, .-arch_rethook_trampoline\n"
    +);
    +NOKPROBE_SYMBOL(arch_rethook_trampoline);
    +/*
    + * arch_rethook_trampoline() skips updating frame pointer. The frame pointer
    + * saved in arch_rethook_trampoline_callback() points to the real caller
    + * function's frame pointer. Thus the arch_rethook_trampoline() doesn't have
    + * a standard stack frame with CONFIG_FRAME_POINTER=y.
    + * Let's mark it non-standard function. Anyway, FP unwinder can correctly
    + * unwind without the hint.
    + */
    +STACK_FRAME_NON_STANDARD_FP(arch_rethook_trampoline);
    +
    +/* This is called from rethook_trampoline_handler(). */
    +void arch_rethook_fixup_return(struct pt_regs *regs,
    + unsigned long correct_ret_addr)
    +{
    + unsigned long *frame_pointer = &regs->sp + 1;
    +
    + /* Replace fake return address with real one. */
    + *frame_pointer = correct_ret_addr;
    +}
    +
    +void arch_rethook_prepare(struct rethook_node *rh, struct pt_regs *regs)
    +{
    + unsigned long *stack = (unsigned long *)regs->sp;
    +
    + rh->ret_addr = stack[0];
    + rh->frame = regs->sp;
    +
    + /* Replace the return addr with trampoline addr */
    + stack[0] = (unsigned long) arch_rethook_trampoline;
    +}
    +NOKPROBE_SYMBOL(arch_rethook_prepare);
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