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SubjectRe: [PATCH 00/20] objtool: UACCESS validation v3
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On March 7, 2019 9:18:29 AM PST, Josh Poimboeuf <jpoimboe@redhat.com> wrote:
>On Thu, Mar 07, 2019 at 09:04:36AM -0800, hpa@zytor.com wrote:
>> On March 7, 2019 8:47:05 AM PST, Josh Poimboeuf <jpoimboe@redhat.com>
>wrote:
>> >On Thu, Mar 07, 2019 at 02:13:12PM +0100, Peter Zijlstra wrote:
>> >> On Thu, Mar 07, 2019 at 01:55:26PM +0100, Peter Zijlstra wrote:
>> >> > On Thu, Mar 07, 2019 at 01:03:17PM +0100, Peter Zijlstra wrote:
>> >>
>> >>
>> >> > > 01be 20d3: 31 c0 xor %eax,%eax
>> >> > > 01c0 20d5: 4c 39 eb cmp %r13,%rbx
>> >> > > 01c3 20d8: 77 08 ja 20e2
>> ><__do_sys_waitid+0x1cd>
>> >>
>> >> randconfig-build/kernel/exit.o: warning: objtool:
>> >__do_sys_waitid()+0x1c3: (branch)
>> >>
>> >> > > 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.
>> >>
>> >> And that is the error, I think. We should've taken it and went to:
>> >>
>> >> return -EFAULT;
>> >>
>> >> because:
>> >>
>> >> +1be xor %eax,%eax eax=0
>> >> +1cd xor $0x1,%eax eax=1
>> >> +1e2 test %al,%al 1&1==1 -> ZF=0
>> >> +1e4 jnz
>> >>
>> >> Is an unconditional code sequence, but there's no way objtool can
>do
>> >> that without becoming a full blown interpreter :/
>> >>
>> >> > > 0213 2128: 49 c7 c7 f2 ff ff ff mov
>> >$0xfffffffffffffff2,%r15
>> >> > > ffffffffffffe0eb }
>> >> > > 021a 212f: 48 8d 65 d8 lea
>-0x28(%rbp),%rsp
>> >> > > 021e 2133: 4c 89 f8 mov %r15,%rax
>> >> > > 0221 2136: 5b pop %rbx
>> >> > > 0222 2137: 41 5c pop %r12
>> >> > > 0224 2139: 41 5d pop %r13
>> >> > > 0226 213b: 41 5e pop %r14
>> >> > > 0228 213d: 41 5f pop %r15
>> >> > > 022a 213f: 5d pop %rbp
>> >> > > 022b 2140: c3 retq
>> >
>> >This "fixes" it, and also seems to help -Os make much code:
>> >
>> >diff --git a/include/linux/compiler.h b/include/linux/compiler.h
>> >index 445348facea9..8de63db58fdd 100644
>> >--- a/include/linux/compiler.h
>> >+++ b/include/linux/compiler.h
>> >@@ -67,7 +67,7 @@ void ftrace_likely_update(struct
>ftrace_likely_data
>> >*f, int val,
>> > .line = __LINE__, \
>> > }; \
>> > ______r = !!(cond); \
>> >- ______f.miss_hit[______r]++; \
>> >+ if (______r) ______f.miss_hit[1]++; else ______f.miss_hit[0]++; \
>> > ______r; \
>> > }))
>> > #endif /* CONFIG_PROFILE_ALL_BRANCHES */
>>
>> if (cond)? Or is ___r used elsewhere?
>
>______r is also the return value. And it's needed because cond should
>only be evaluated once.

So put a true; and false; inside the if.
--
Sent from my Android device with K-9 Mail. Please excuse my brevity.

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