On Tue, May 07, 2019 at 01:42:29PM -0400, Steven Rostedt wrote: > 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.
This part is done by patch 1. > > The helper functions were also added: No longer "also" :-) > 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; > +} How this works isn't really obvious. A comment is probably warranted to explain the fact that the int3 entry code reserved some space on the stack. -- Josh
