On Thu, Mar 07, 2019 at 01:03:17PM +0100, Peter Zijlstra wrote:
> 01c3 20d8: 77 08 ja 20e2
> <__do_sys_waitid+0x1cd>
taken:
randconfig-build/kernel/exit.o: warning: objtool: __do_sys_waitid()+0x1c3:
(branch)
> ffffffffffffe0f5 alternative("", __stringify(__ASM_STAC),
> X86_FEATURE_SMAP);
> 01c8 20dd: 90 nop
> 01c9 20de: 90 nop
> 01ca 20df: 90 nop
Bye-bye STAC, jumped straight over.
> 01cd 20e2: 83 f0 01 xor $0x1,%eax
> 01d0 20e5: 48 89 c2 mov %rax,%rdx
> 01d3 20e8: 83 e2 01 and $0x1,%edx
> 01d6 20eb: 48 83 c2 02 add $0x2,%rdx
> 01da 20ef: 48 ff 04 d5 00 00 00 incq 0x0(,%rdx,8)
> 01e1 20f6: 00
> 01de 20f3: R_X86_64_32S _ftrace_branch+0x148
> 01e2 20f7: 84 c0 test %al,%al
> 01e4 20f9: 75 2d jne 2128
> <__do_sys_waitid+0x213>
we do not take this branch and fall-through.
> ffffffffffffe0eb return -EFAULT;
> ffffffffffffe0eb
> ffffffffffffe0eb unsafe_put_user(signo, &infop->si_signo, Efault);
> 01e6 20fb: 44 89 33 mov %r14d,(%rbx)
fault, take exception:
randconfig-build/kernel/exit.o: warning: objtool: __do_sys_waitid()+0x1e6:
(alt)
Relocation section '.rela__ex_table' at offset 0x21568 contains 18 entries:
Offset Info Type Sym. Value Sym. Name + Addend
000000000000 000200000002 R_X86_64_PC32 0000000000000000 .text + 20fb
000000000004 000200000002 R_X86_64_PC32 0000000000000000 .text + 2125
> ffffffffffffefe5 Efault:
> ffffffffffffe0eb user_access_end();
> 0210 2125: 90 nop
> 0211 2126: 90 nop
> 0212 2127: 90 nop
randconfig-build/kernel/exit.o: warning: objtool: __do_sys_waitid()+0x210:
(alt)
000000000034 000200000002 R_X86_64_PC32 0000000000000000 .text + 2125
000000000038 00c800000002 R_X86_64_PC32 0000000000000000
.altinstr_replacement + c
0000000000000000 <.altinstr_replacement>:
c: 0f 01 ca clac
randconfig-build/kernel/exit.o: warning: objtool: .altinstr_replacement+0xc:
redundant UACCESS disable
