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    Subject[PATCH 5.0 065/139] x86_64: Allow breakpoints to emulate call instructions
    Date
    From: Peter Zijlstra <peterz@infradead.org>

    commit 4b33dadf37666c0860b88f9e52a16d07bf6d0b03 upstream.

    In order to allow breakpoints to emulate call instructions, they need to push
    the return address onto the stack. The x86_64 int3 handler adds a small gap
    to allow the stack to grow some. Use this gap to add the return address to
    be able to emulate a call instruction at the breakpoint location.

    These helper functions are added:

    int3_emulate_jmp(): changes the location of the regs->ip to return there.

    (The next two are only for x86_64)
    int3_emulate_push(): to push the address onto the gap in the stack
    int3_emulate_call(): push the return address and change regs->ip

    Cc: Andy Lutomirski <luto@kernel.org>
    Cc: Nicolai Stange <nstange@suse.de>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Cc: Ingo Molnar <mingo@redhat.com>
    Cc: Borislav Petkov <bp@alien8.de>
    Cc: "H. Peter Anvin" <hpa@zytor.com>
    Cc: the arch/x86 maintainers <x86@kernel.org>
    Cc: Josh Poimboeuf <jpoimboe@redhat.com>
    Cc: Jiri Kosina <jikos@kernel.org>
    Cc: Miroslav Benes <mbenes@suse.cz>
    Cc: Petr Mladek <pmladek@suse.com>
    Cc: Joe Lawrence <joe.lawrence@redhat.com>
    Cc: Shuah Khan <shuah@kernel.org>
    Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
    Cc: Tim Chen <tim.c.chen@linux.intel.com>
    Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
    Cc: Mimi Zohar <zohar@linux.ibm.com>
    Cc: Juergen Gross <jgross@suse.com>
    Cc: Nick Desaulniers <ndesaulniers@google.com>
    Cc: Nayna Jain <nayna@linux.ibm.com>
    Cc: Masahiro Yamada <yamada.masahiro@socionext.com>
    Cc: Joerg Roedel <jroedel@suse.de>
    Cc: "open list:KERNEL SELFTEST FRAMEWORK" <linux-kselftest@vger.kernel.org>
    Cc: stable@vger.kernel.org
    Fixes: b700e7f03df5 ("livepatch: kernel: add support for live patching")
    Tested-by: Nicolai Stange <nstange@suse.de>
    Reviewed-by: Nicolai Stange <nstange@suse.de>
    Reviewed-by: Masami Hiramatsu <mhiramat@kernel.org>
    Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
    [ Modified to only work for x86_64 and added comment to int3_emulate_push() ]
    Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    arch/x86/include/asm/text-patching.h | 28 ++++++++++++++++++++++++++++
    1 file changed, 28 insertions(+)

    --- a/arch/x86/include/asm/text-patching.h
    +++ b/arch/x86/include/asm/text-patching.h
    @@ -39,4 +39,32 @@ extern int poke_int3_handler(struct pt_r
    extern void *text_poke_bp(void *addr, const void *opcode, size_t len, void *handler);
    extern int after_bootmem;

    +static inline void int3_emulate_jmp(struct pt_regs *regs, unsigned long ip)
    +{
    + regs->ip = ip;
    +}
    +
    +#define INT3_INSN_SIZE 1
    +#define CALL_INSN_SIZE 5
    +
    +#ifdef CONFIG_X86_64
    +static inline void int3_emulate_push(struct pt_regs *regs, unsigned long val)
    +{
    + /*
    + * The int3 handler in entry_64.S adds a gap between the
    + * stack where the break point happened, and the saving of
    + * pt_regs. We can extend the original stack because of
    + * this gap. See the idtentry macro's create_gap option.
    + */
    + regs->sp -= sizeof(unsigned long);
    + *(unsigned long *)regs->sp = val;
    +}
    +
    +static inline void int3_emulate_call(struct pt_regs *regs, unsigned long func)
    +{
    + int3_emulate_push(regs, regs->ip - INT3_INSN_SIZE + CALL_INSN_SIZE);
    + int3_emulate_jmp(regs, func);
    +}
    +#endif
    +
    #endif /* _ASM_X86_TEXT_PATCHING_H */

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