Messages in this thread | | | Date | Thu, 29 Nov 2018 10:42:10 +0100 | From | Peter Zijlstra <> | Subject | Re: [PATCH v2 4/4] x86/static_call: Add inline static call implementation for x86-64 |
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On Wed, Nov 28, 2018 at 10:05:54PM -0800, Andy Lutomirski wrote:
> >> +static void static_call_bp_handler(struct pt_regs *regs, void *_data) > >> +{ > >> + struct static_call_bp_data *data = _data; > >> + > >> + /* > >> + * For inline static calls, push the return address on the stack so the > >> + * "called" function will return to the location immediately after the > >> + * call site. > >> + * > >> + * NOTE: This code will need to be revisited when kernel CET gets > >> + * implemented. > >> + */ > >> + if (data->ret) { > >> + regs->sp -= sizeof(long); > >> + *(unsigned long *)regs->sp = data->ret; > >> + } > > You can’t do this. Depending on the alignment of the old RSP, which > is not guaranteed, this overwrites regs->cs. IRET goes boom.
I don't get it; can you spell that out?
The way I understand it is that we're at a location where a "E8 - Near CALL" instruction should be, and thus RSP should be the regular kernel stack, and the above simply does "PUSH ret", which is what that CALL would've done too.
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