Messages in this thread | | | Subject | Re: [PATCH][v2] uprobes/x86: emulate push insns for uprobe on x86 | From | Yonghong Song <> | Date | Mon, 13 Nov 2017 12:32:18 -0800 |
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On 11/13/17 4:59 AM, Oleg Nesterov wrote: > The patch looks good to me, but I have a question because I know nothing > about insn encoding, > > On 11/10, Yonghong Song wrote: >> >> +static int push_setup_xol_ops(struct arch_uprobe *auprobe, struct insn *insn) >> +{ >> + u8 opc1 = OPCODE1(insn), reg_offset = 0; >> + >> + if (opc1 < 0x50 || opc1 > 0x57) >> + return -ENOSYS; >> + >> + if (insn->length > 2) >> + return -ENOSYS; >> + if (insn->length == 2) { >> + /* only support rex_prefix 0x41 (x64 only) */ >> +#ifdef CONFIG_X86_64 >> + if (insn->rex_prefix.nbytes != 1 || >> + insn->rex_prefix.bytes[0] != 0x41) >> + return -ENOSYS; >> + >> + auprobe->push.ilen = 2; > > and the "else" branch does > > auprobe->push.ilen = 1; > > you could add > auprobe->push.ilen = insn->length; > > at the end of push_setup_xol_ops() instead, but this is minor/cosmetic,
Will make this change in the next revision.
> > >> + switch (opc1) { >> + case 0x50: >> + reg_offset = offsetof(struct pt_regs, r8); >> + break; >> + case 0x51: >> + reg_offset = offsetof(struct pt_regs, r9); >> + break; >> + case 0x52: >> + reg_offset = offsetof(struct pt_regs, r10); >> + break; >> + case 0x53: >> + reg_offset = offsetof(struct pt_regs, r11); >> + break; >> + case 0x54: >> + reg_offset = offsetof(struct pt_regs, r12); >> + break; >> + case 0x55: >> + reg_offset = offsetof(struct pt_regs, r13); >> + break; >> + case 0x56: >> + reg_offset = offsetof(struct pt_regs, r14); >> + break; >> + case 0x57: >> + reg_offset = offsetof(struct pt_regs, r15); >> + break; >> + } >> +#else >> + return -ENOSYS; >> +#endif > > OK, but shouldn't we also return ENOSYS if CONFIG_X86_64=y but the probed task is 32bit?
Just tested with a 32bit app on x86 box and segfaults. Yes, we would need to return ENOSYS if the app is 32bit on 64bit system. I may not be worthwhile to emulate this uncommon case.
I will use mmap_is_ia32 or a variant to test whether the app is 32bit or not. Please let me know whether this is correct approach or not.
> > Or in this case uprobe_init_insn(x86_64 => false) should fail and push_setup_xol_ops() > won't be called? > > Oleg. >
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