From: Peter Zijlstra <[email protected]> In order to allow breakpoints to emulate call functions, they need to push the return address onto the stack. But because the breakpoint exception frame is added to the stack when the breakpoint is hit, there's no room to add the address onto the stack and return to the address of the emulated called funtion.
To handle this, copy the exception frame on entry of the breakpoint handler and have leave a gap that can be used to add a return address to the stack frame and return from the breakpoint to the emulated called function, allowing for that called function to return back to the location after the breakpoint was placed. The helper functions were also added: int3_emulate_push(): to push the address onto the gap in the stack int3_emulate_jmp(): changes the location of the regs->ip to return there. int3_emulate_call(): push the return address and change regs->ip Cc: Andy Lutomirski <[email protected]> Cc: Nicolai Stange <[email protected]> Cc: Thomas Gleixner <[email protected]> Cc: Ingo Molnar <[email protected]> Cc: Borislav Petkov <[email protected]> Cc: "H. Peter Anvin" <[email protected]> Cc: the arch/x86 maintainers <[email protected]> Cc: Josh Poimboeuf <[email protected]> Cc: Jiri Kosina <[email protected]> Cc: Miroslav Benes <[email protected]> Cc: Petr Mladek <[email protected]> Cc: Joe Lawrence <[email protected]> Cc: Shuah Khan <[email protected]> Cc: Konrad Rzeszutek Wilk <[email protected]> Cc: Tim Chen <[email protected]> Cc: Sebastian Andrzej Siewior <[email protected]> Cc: Mimi Zohar <[email protected]> Cc: Juergen Gross <[email protected]> Cc: Nick Desaulniers <[email protected]> Cc: Nayna Jain <[email protected]> Cc: Masahiro Yamada <[email protected]> Cc: Joerg Roedel <[email protected]> Cc: "open list:KERNEL SELFTEST FRAMEWORK" <[email protected]> Cc: [email protected] Fixes: b700e7f03df5 ("livepatch: kernel: add support for live patching") Signed-off-by: Peter Zijlstra (Intel) <[email protected]> [ Modified to only work for x86_64 ] Signed-off-by: Steven Rostedt (VMware) <[email protected]> --- arch/x86/include/asm/text-patching.h | 22 ++++++++++++++++++++++ 1 file changed, 22 insertions(+) diff --git a/arch/x86/include/asm/text-patching.h b/arch/x86/include/asm/text-patching.h index e85ff65c43c3..455bf9f88233 100644 --- a/arch/x86/include/asm/text-patching.h +++ b/arch/x86/include/asm/text-patching.h @@ -39,4 +39,26 @@ extern int poke_int3_handler(struct pt_regs *regs); 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) +{ + 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 */ -- 2.20.1
