Re: linux-next: build warnings after merge of the block tree

From: Josh Poimboeuf
Date: Tue Apr 11 2023 - 20:14:10 EST

On Tue, Apr 11, 2023 at 04:39:39PM -0600, Jens Axboe wrote:
> >>>>> lib/iov_iter.o: warning: objtool: .altinstr_replacement+0x0: redundant UACCESS d
> >>>>> isable
> >>>>> lib/iov_iter.o: warning: objtool: iovec_from_user.part.0+0xc7: call to copy_comp
> >>>>> at_iovec_from_user.part.0() with UACCESS enabled
> >>>>> lib/iov_iter.o: warning: objtool: __import_iovec+0x21d: call to copy_compat_iovec_from_user.part.0() with UACCESS enabled
> >>>>>
> >>>>> Presumably introduced by commit
> >>>>>
> >>>>> 6376ce56feb6 ("iov_iter: import single vector iovecs as ITER_UBUF")
>
> lib/iov_iter.o attached, gzip'ed. NOTE: if you disable either of the
> copy_compat_iovec_from_user() as per diff below (commented out), then
> it doesn't complain. Is there some bug where it thinks we'll hit both?
> That should not be possible.

Yeah, the problem is an inter-procedural compiler optimization which
moves the user_access_begin() out of copy_compat_iovec_from_user() and
into its callers.

Which is fine, but objtool doesn't like it as it expects the uaccess
enable to not cross function boundaries.

Do the warnings go away if you make copy_compat_iovec_from_user()
non-static?

Peter, what do you think, should we make track uaccess state across
function boundaries?

Disassembly below:


0000000000000730 <copy_compat_iovec_from_user.part.0>:
730: 48 85 d2 test %rdx,%rdx
733: 74 45 je 77a <copy_compat_iovec_from_user.part.0+0x4a>

735: 45 31 c9 xor %r9d,%r9d
738: 31 c0 xor %eax,%eax
73a: eb 1d jmp 759 <copy_compat_iovec_from_user.part.0+0x29>

73c: 48 c1 e0 04 shl $0x4,%rax
740: 41 83 c1 01 add $0x1,%r9d
744: 48 01 f8 add %rdi,%rax
747: 48 89 08 mov %rcx,(%rax)
74a: 44 89 c1 mov %r8d,%ecx
74d: 48 89 48 08 mov %rcx,0x8(%rax)
751: 49 63 c1 movslq %r9d,%rax
754: 48 39 d0 cmp %rdx,%rax
757: 73 21 jae 77a <copy_compat_iovec_from_user.part.0+0x4a>

759: 48 8d 0c c6 lea (%rsi,%rax,8),%rcx
75d: 44 8b 41 04 mov 0x4(%rcx),%r8d
761: 8b 09 mov (%rcx),%ecx
763: 89 c9 mov %ecx,%ecx
765: 45 85 c0 test %r8d,%r8d
768: 79 d2 jns 73c <copy_compat_iovec_from_user.part.0+0xc>

76a: b8 ea ff ff ff mov $0xffffffea,%eax
76f: 90 nop
770: 90 nop
771: 90 nop
772: c3 ret

773: b8 f2 ff ff ff mov $0xfffffff2,%eax
778: eb f5 jmp 76f <copy_compat_iovec_from_user.part.0+0x3f>

77a: 31 c0 xor %eax,%eax
77c: eb f1 jmp 76f <copy_compat_iovec_from_user.part.0+0x3f>

77e: 66 90 xchg %ax,%ax

0000000000002380 <iovec_from_user.part.0>:
2380: 41 56 push %r14
2382: 45 89 c6 mov %r8d,%r14d
2385: 41 55 push %r13
2387: 49 89 fd mov %rdi,%r13
238a: 41 54 push %r12
238c: 49 89 cc mov %rcx,%r12
238f: 55 push %rbp
2390: 48 89 cd mov %rcx,%rbp
2393: 53 push %rbx
2394: 48 89 f3 mov %rsi,%rbx
2397: 48 83 ec 08 sub $0x8,%rsp
239b: 48 39 f2 cmp %rsi,%rdx
239e: 0f 82 bc 00 00 00 jb 2460 <iovec_from_user.part.0+0xe0>
23a4: 45 84 f6 test %r14b,%r14b
23a7: 75 70 jne 2419 <iovec_from_user.part.0+0x99>
23a9: 48 89 da mov %rbx,%rdx
23ac: 48 c1 e2 04 shl $0x4,%rdx
23b0: 48 81 fa ff ff ff 7f cmp $0x7fffffff,%rdx
23b7: 0f 87 98 00 00 00 ja 2455 <iovec_from_user.part.0+0xd5>
23bd: 4c 89 ee mov %r13,%rsi
23c0: 48 89 ef mov %rbp,%rdi
23c3: e8 00 00 00 00 call 23c8 <iovec_from_user.part.0+0x48> 23c4: R_X86_64_PLT32 _copy_from_user-0x4
23c8: 48 85 c0 test %rax,%rax
23cb: 0f 85 86 00 00 00 jne 2457 <iovec_from_user.part.0+0xd7>
23d1: 48 85 db test %rbx,%rbx
23d4: 75 0b jne 23e1 <iovec_from_user.part.0+0x61>
23d6: eb 78 jmp 2450 <iovec_from_user.part.0+0xd0>
23d8: 48 83 c0 01 add $0x1,%rax
23dc: 48 39 c3 cmp %rax,%rbx
23df: 74 6f je 2450 <iovec_from_user.part.0+0xd0>
23e1: 48 89 c2 mov %rax,%rdx
23e4: 48 c1 e2 04 shl $0x4,%rdx
23e8: 48 83 7c 15 08 00 cmpq $0x0,0x8(%rbp,%rdx,1)
23ee: 79 e8 jns 23d8 <iovec_from_user.part.0+0x58>
23f0: b8 ea ff ff ff mov $0xffffffea,%eax
23f5: 48 98 cltq
23f7: 4c 39 e5 cmp %r12,%rbp
23fa: 74 10 je 240c <iovec_from_user.part.0+0x8c>
23fc: 48 89 ef mov %rbp,%rdi
23ff: 48 89 04 24 mov %rax,(%rsp)
2403: e8 00 00 00 00 call 2408 <iovec_from_user.part.0+0x88> 2404: R_X86_64_PLT32 kfree-0x4
2408: 48 8b 04 24 mov (%rsp),%rax
240c: 48 83 c4 08 add $0x8,%rsp
2410: 5b pop %rbx
2411: 5d pop %rbp
2412: 41 5c pop %r12
2414: 41 5d pop %r13
2416: 41 5e pop %r14
2418: c3 ret
2419: 48 8d 14 dd 00 00 00 00 lea 0x0(,%rbx,8),%rdx
2421: 48 b8 00 f0 ff ff ff 7f 00 00 movabs $0x7ffffffff000,%rax
242b: 48 39 d0 cmp %rdx,%rax
242e: 72 27 jb 2457 <iovec_from_user.part.0+0xd7>
2430: 48 29 d0 sub %rdx,%rax
2433: 4c 39 e8 cmp %r13,%rax
2436: 72 1f jb 2457 <iovec_from_user.part.0+0xd7>
2438: 90 nop
2439: 90 nop
243a: 90 nop
243b: 90 nop
243c: 90 nop
243d: 90 nop
243e: 48 89 da mov %rbx,%rdx
2441: 4c 89 ee mov %r13,%rsi
2444: 48 89 ef mov %rbp,%rdi
2447: e8 e4 e2 ff ff call 730 <copy_compat_iovec_from_user.part.0>
244c: 85 c0 test %eax,%eax
244e: 75 a5 jne 23f5 <iovec_from_user.part.0+0x75>
2450: 48 89 e8 mov %rbp,%rax
2453: eb b7 jmp 240c <iovec_from_user.part.0+0x8c>
2455: 0f 0b ud2
2457: 48 c7 c0 f2 ff ff ff mov $0xfffffffffffffff2,%rax
245e: eb 97 jmp 23f7 <iovec_from_user.part.0+0x77>
2460: 48 89 f7 mov %rsi,%rdi
2463: 48 89 f0 mov %rsi,%rax
2466: 48 c1 e7 04 shl $0x4,%rdi
246a: 48 c1 e8 3c shr $0x3c,%rax
246e: 75 16 jne 2486 <iovec_from_user.part.0+0x106>
2470: be c0 0c 00 00 mov $0xcc0,%esi
2475: e8 00 00 00 00 call 247a <iovec_from_user.part.0+0xfa> 2476: R_X86_64_PLT32 __kmalloc-0x4
247a: 48 89 c5 mov %rax,%rbp
247d: 48 85 c0 test %rax,%rax
2480: 0f 85 1e ff ff ff jne 23a4 <iovec_from_user.part.0+0x24>
2486: 48 c7 c0 f4 ff ff ff mov $0xfffffffffffffff4,%rax
248d: e9 7a ff ff ff jmp 240c <iovec_from_user.part.0+0x8c>
2492: 66 66 2e 0f 1f 84 00 00 00 00 00 data16 cs nopw 0x0(%rax,%rax,1)
249d: 0f 1f 00 nopl (%rax)

0000000000004910 <__import_iovec>:
4910: 41 56 push %r14
4912: 4d 89 ce mov %r9,%r14
4915: 41 55 push %r13
4917: 41 89 fd mov %edi,%r13d
491a: 48 89 f7 mov %rsi,%rdi
491d: 41 54 push %r12
491f: 55 push %rbp
4920: 4c 89 c5 mov %r8,%rbp
4923: 53 push %rbx
4924: 44 8b 44 24 30 mov 0x30(%rsp),%r8d
4929: 48 8b 5d 00 mov 0x0(%rbp),%rbx
492d: 83 fa 01 cmp $0x1,%edx
4930: 0f 84 18 01 00 00 je 4a4e <__import_iovec+0x13e>
4936: 41 89 d4 mov %edx,%r12d
4939: 4d 85 e4 test %r12,%r12
493c: 0f 84 f7 00 00 00 je 4a39 <__import_iovec+0x129>
4942: 49 81 fc 00 04 00 00 cmp $0x400,%r12
4949: 0f 87 ad 01 00 00 ja 4afc <__import_iovec+0x1ec>
494f: 89 ca mov %ecx,%edx
4951: 45 0f b6 c0 movzbl %r8b,%r8d
4955: 48 89 d9 mov %rbx,%rcx
4958: 4c 89 e6 mov %r12,%rsi
495b: e8 20 da ff ff call 2380 <iovec_from_user.part.0>
4960: 4d 89 e0 mov %r12,%r8
4963: 31 c9 xor %ecx,%ecx
4965: 41 ba 00 f0 ff 7f mov $0x7ffff000,%r10d
496b: 49 c1 e0 04 shl $0x4,%r8
496f: 48 89 c3 mov %rax,%rbx
4972: 48 bf 00 f0 ff ff ff 7f 00 00 movabs $0x7ffffffff000,%rdi
497c: 49 01 c0 add %rax,%r8
497f: 48 3d 00 f0 ff ff cmp $0xfffffffffffff000,%rax
4985: 0f 87 bb 00 00 00 ja 4a46 <__import_iovec+0x136>
498b: 48 8b 50 08 mov 0x8(%rax),%rdx
498f: 48 8b 30 mov (%rax),%rsi
4992: 48 39 d7 cmp %rdx,%rdi
4995: 72 0b jb 49a2 <__import_iovec+0x92>
4997: 49 89 f9 mov %rdi,%r9
499a: 49 29 d1 sub %rdx,%r9
499d: 49 39 f1 cmp %rsi,%r9
49a0: 73 29 jae 49cb <__import_iovec+0xbb>
49a2: 48 39 5d 00 cmp %rbx,0x0(%rbp)
49a6: 74 08 je 49b0 <__import_iovec+0xa0>
49a8: 48 89 df mov %rbx,%rdi
49ab: e8 00 00 00 00 call 49b0 <__import_iovec+0xa0> 49ac: R_X86_64_PLT32 kfree-0x4
49b0: 48 c7 45 00 00 00 00 00 movq $0x0,0x0(%rbp)
49b8: 48 c7 c1 f2 ff ff ff mov $0xfffffffffffffff2,%rcx
49bf: 5b pop %rbx
49c0: 48 89 c8 mov %rcx,%rax
49c3: 5d pop %rbp
49c4: 41 5c pop %r12
49c6: 41 5d pop %r13
49c8: 41 5e pop %r14
49ca: c3 ret
49cb: 4c 89 d6 mov %r10,%rsi
49ce: 48 29 ce sub %rcx,%rsi
49d1: 48 01 d1 add %rdx,%rcx
49d4: 48 39 d6 cmp %rdx,%rsi
49d7: 73 09 jae 49e2 <__import_iovec+0xd2>
49d9: 48 89 70 08 mov %rsi,0x8(%rax)
49dd: b9 00 f0 ff 7f mov $0x7ffff000,%ecx
49e2: 48 83 c0 10 add $0x10,%rax
49e6: 49 39 c0 cmp %rax,%r8
49e9: 75 a0 jne 498b <__import_iovec+0x7b>
49eb: 48 89 c8 mov %rcx,%rax
49ee: 41 83 fd 01 cmp $0x1,%r13d
49f2: 0f 87 5f 01 00 00 ja 4b57 <__import_iovec+0x247>
49f8: 31 d2 xor %edx,%edx
49fa: 45 85 ed test %r13d,%r13d
49fd: 49 89 5e 10 mov %rbx,0x10(%r14)
4a01: 49 89 46 18 mov %rax,0x18(%r14)
4a05: 41 0f 95 46 02 setne 0x2(%r14)
4a0a: 31 c0 xor %eax,%eax
4a0c: 66 41 89 16 mov %dx,(%r14)
4a10: 41 c6 46 03 01 movb $0x1,0x3(%r14)
4a15: 49 c7 46 08 00 00 00 00 movq $0x0,0x8(%r14)
4a1d: 4d 89 66 20 mov %r12,0x20(%r14)
4a21: 48 39 5d 00 cmp %rbx,0x0(%rbp)
4a25: 48 0f 44 d8 cmove %rax,%rbx
4a29: 48 89 c8 mov %rcx,%rax
4a2c: 48 89 5d 00 mov %rbx,0x0(%rbp)
4a30: 5b pop %rbx
4a31: 5d pop %rbp
4a32: 41 5c pop %r12
4a34: 41 5d pop %r13
4a36: 41 5e pop %r14
4a38: c3 ret
4a39: 31 c0 xor %eax,%eax
4a3b: 31 c9 xor %ecx,%ecx
4a3d: 48 81 fb 00 f0 ff ff cmp $0xfffffffffffff000,%rbx
4a44: 76 a8 jbe 49ee <__import_iovec+0xde>
4a46: 48 89 d9 mov %rbx,%rcx
4a49: e9 b5 00 00 00 jmp 4b03 <__import_iovec+0x1f3>
4a4e: 45 84 c0 test %r8b,%r8b
4a51: 0f 85 b9 00 00 00 jne 4b10 <__import_iovec+0x200>
4a57: ba 10 00 00 00 mov $0x10,%edx
4a5c: 48 89 df mov %rbx,%rdi
4a5f: e8 00 00 00 00 call 4a64 <__import_iovec+0x154> 4a60: R_X86_64_PLT32 _copy_from_user-0x4
4a64: 48 85 c0 test %rax,%rax
4a67: 0f 85 4b ff ff ff jne 49b8 <__import_iovec+0xa8>
4a6d: 48 8b 43 08 mov 0x8(%rbx),%rax
4a71: 48 85 c0 test %rax,%rax
4a74: 0f 88 d1 00 00 00 js 4b4b <__import_iovec+0x23b>
4a7a: 48 ba 00 f0 ff ff ff 7f 00 00 movabs $0x7ffffffff000,%rdx
4a84: 48 8b 0b mov (%rbx),%rcx
4a87: 48 29 c2 sub %rax,%rdx
4a8a: 48 3d 00 f0 ff 7f cmp $0x7ffff000,%rax
4a90: 76 0f jbe 4aa1 <__import_iovec+0x191>
4a92: 48 ba 00 00 00 80 ff 7f 00 00 movabs $0x7fff80000000,%rdx
4a9c: b8 00 f0 ff 7f mov $0x7ffff000,%eax
4aa1: 48 39 ca cmp %rcx,%rdx
4aa4: 0f 82 0e ff ff ff jb 49b8 <__import_iovec+0xa8>
4aaa: 41 83 fd 01 cmp $0x1,%r13d
4aae: 0f 87 aa 00 00 00 ja 4b5e <__import_iovec+0x24e>
4ab4: 45 85 ed test %r13d,%r13d
4ab7: 49 c7 06 00 00 00 00 movq $0x0,(%r14)
4abe: 49 89 46 18 mov %rax,0x18(%r14)
4ac2: 49 89 4e 10 mov %rcx,0x10(%r14)
4ac6: 49 c7 46 08 00 00 00 00 movq $0x0,0x8(%r14)
4ace: 41 c6 06 05 movb $0x5,(%r14)
4ad2: 41 c6 46 03 01 movb $0x1,0x3(%r14)
4ad7: 49 c7 46 20 01 00 00 00 movq $0x1,0x20(%r14)
4adf: 41 0f 95 46 02 setne 0x2(%r14)
4ae4: 48 c7 45 00 00 00 00 00 movq $0x0,0x0(%rbp)
4aec: 49 8b 4e 18 mov 0x18(%r14),%rcx
4af0: 5b pop %rbx
4af1: 5d pop %rbp
4af2: 48 89 c8 mov %rcx,%rax
4af5: 41 5c pop %r12
4af7: 41 5d pop %r13
4af9: 41 5e pop %r14
4afb: c3 ret
4afc: 48 c7 c1 ea ff ff ff mov $0xffffffffffffffea,%rcx
4b03: 48 c7 45 00 00 00 00 00 movq $0x0,0x0(%rbp)
4b0b: e9 af fe ff ff jmp 49bf <__import_iovec+0xaf>
4b10: 48 b8 f8 ef ff ff ff 7f 00 00 movabs $0x7fffffffeff8,%rax
4b1a: 48 39 f0 cmp %rsi,%rax
4b1d: 0f 82 95 fe ff ff jb 49b8 <__import_iovec+0xa8>
4b23: 90 nop
4b24: 90 nop
4b25: 90 nop
4b26: 90 nop
4b27: 90 nop
4b28: 90 nop
4b29: ba 01 00 00 00 mov $0x1,%edx
4b2e: 48 89 df mov %rbx,%rdi
4b31: e8 fa bb ff ff call 730 <copy_compat_iovec_from_user.part.0>
4b36: 48 63 c8 movslq %eax,%rcx
4b39: 48 85 c9 test %rcx,%rcx
4b3c: 0f 85 7d fe ff ff jne 49bf <__import_iovec+0xaf>
4b42: 48 8b 43 08 mov 0x8(%rbx),%rax
4b46: e9 2f ff ff ff jmp 4a7a <__import_iovec+0x16a>
4b4b: 48 c7 c1 ea ff ff ff mov $0xffffffffffffffea,%rcx
4b52: e9 68 fe ff ff jmp 49bf <__import_iovec+0xaf>
4b57: 0f 0b ud2
4b59: e9 9a fe ff ff jmp 49f8 <__import_iovec+0xe8>
4b5e: 0f 0b ud2
4b60: e9 4f ff ff ff jmp 4ab4 <__import_iovec+0x1a4>
4b65: 66 66 2e 0f 1f 84 00 00 00 00 00 data16 cs nopw 0x0(%rax,%rax,1)

--
Josh