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e65050b94d
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Josh Poimboeuf e65050b94d objtool: Fix seg fault on bad switch table entry 
In one rare case, Clang generated the following code:

 5ca:       83 e0 21                and    $0x21,%eax
 5cd:       b9 04 00 00 00          mov    $0x4,%ecx
 5d2:       ff 24 c5 00 00 00 00    jmpq   *0x0(,%rax,8)
                    5d5: R_X86_64_32S       .rodata+0x38

which uses the corresponding jump table relocations:

  000000000038  000200000001 R_X86_64_64       0000000000000000 .text + 834
  000000000040  000200000001 R_X86_64_64       0000000000000000 .text + 5d9
  000000000048  000200000001 R_X86_64_64       0000000000000000 .text + b96
  000000000050  000200000001 R_X86_64_64       0000000000000000 .text + b96
  000000000058  000200000001 R_X86_64_64       0000000000000000 .text + b96
  000000000060  000200000001 R_X86_64_64       0000000000000000 .text + b96
  000000000068  000200000001 R_X86_64_64       0000000000000000 .text + b96
  000000000070  000200000001 R_X86_64_64       0000000000000000 .text + b96
  000000000078  000200000001 R_X86_64_64       0000000000000000 .text + b96
  000000000080  000200000001 R_X86_64_64       0000000000000000 .text + b96
  000000000088  000200000001 R_X86_64_64       0000000000000000 .text + b96
  000000000090  000200000001 R_X86_64_64       0000000000000000 .text + b96
  000000000098  000200000001 R_X86_64_64       0000000000000000 .text + b96
  0000000000a0  000200000001 R_X86_64_64       0000000000000000 .text + b96
  0000000000a8  000200000001 R_X86_64_64       0000000000000000 .text + b96
  0000000000b0  000200000001 R_X86_64_64       0000000000000000 .text + b96
  0000000000b8  000200000001 R_X86_64_64       0000000000000000 .text + b96
  0000000000c0  000200000001 R_X86_64_64       0000000000000000 .text + b96
  0000000000c8  000200000001 R_X86_64_64       0000000000000000 .text + b96
  0000000000d0  000200000001 R_X86_64_64       0000000000000000 .text + b96
  0000000000d8  000200000001 R_X86_64_64       0000000000000000 .text + b96
  0000000000e0  000200000001 R_X86_64_64       0000000000000000 .text + b96
  0000000000e8  000200000001 R_X86_64_64       0000000000000000 .text + b96
  0000000000f0  000200000001 R_X86_64_64       0000000000000000 .text + b96
  0000000000f8  000200000001 R_X86_64_64       0000000000000000 .text + b96
  000000000100  000200000001 R_X86_64_64       0000000000000000 .text + b96
  000000000108  000200000001 R_X86_64_64       0000000000000000 .text + b96
  000000000110  000200000001 R_X86_64_64       0000000000000000 .text + b96
  000000000118  000200000001 R_X86_64_64       0000000000000000 .text + b96
  000000000120  000200000001 R_X86_64_64       0000000000000000 .text + b96
  000000000128  000200000001 R_X86_64_64       0000000000000000 .text + b96
  000000000130  000200000001 R_X86_64_64       0000000000000000 .text + b96
  000000000138  000200000001 R_X86_64_64       0000000000000000 .text + 82f
  000000000140  000200000001 R_X86_64_64       0000000000000000 .text + 828

Since %eax was masked with 0x21, only the first two and the last two
entries are possible.

Objtool doesn't actually emulate all the code, so it isn't smart enough
to know that all the middle entries aren't reachable.  They point to the
NOP padding area after the end of the function, so objtool seg faulted
when it tried to dereference a NULL insn->func.

After this fix, objtool still gives an "unreachable" error because it
stops reading the jump table when it encounters the bad addresses:

  /home/jpoimboe/objtool-tests/adm1275.o: warning: objtool: adm1275_probe()+0x828: unreachable instruction

While the above code is technically correct, it's very wasteful of
memory -- it uses 34 jump table entries when only 4 are needed.  It's
also not possible for objtool to validate this type of switch table
because the unused entries point outside the function and objtool has no
way of determining if that's intentional.  Hopefully the Clang folks can
fix it.

Reported-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Nick Desaulniers <ndesaulniers@google.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/a9db88eec4f1ca089e040989846961748238b6d8.1563413318.git.jpoimboe@redhat.com
2019-07-18 21:01:10 +02:00
..
accounting
arch tools arch x86: Sync asm/cpufeatures.h with the with the kernel 2019-07-08 13:47:14 -03:00
bpf Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2019-07-08 19:48:57 -07:00
build tools build: Check if gettid() is available before providing helper 2019-07-07 17:53:09 -03:00
cgroup
crypto
debugging tools: add a kernel-chktaint to tools/debugging 2019-01-08 16:29:52 -07:00
firewire treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 156 2019-05-30 11:26:35 -07:00
firmware Driver Core and debugfs changes for 5.3-rc1 2019-07-12 12:24:03 -07:00
gpio Bulk GPIO changes for the v5.3 kernel cycle: 2019-07-09 09:07:00 -07:00
hv treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 280 2019-06-05 17:36:36 +02:00
iio Second set of IIO device support, features, cleanups and minor fixes for 5.3. 2019-07-01 10:58:13 +02:00
include docs: cgroup-v1: add it to the admin-guide book 2019-07-15 11:03:02 -03:00
io_uring tools/io_uring: sync with liburing 2019-05-23 10:25:26 -06:00
kvm/kvm_stat treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 499 2019-06-19 17:09:53 +02:00
laptop treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 505 2019-06-19 17:11:22 +02:00
leds
lib perf/core improvements and fixes: 2019-07-13 11:12:47 +02:00
memory-model tools/memory-model: Improve data-race detection 2019-06-24 09:08:54 -07:00
nfsd
objtool objtool: Fix seg fault on bad switch table entry 2019-07-18 21:01:10 +02:00
pci pci-v5.3-changes 2019-07-15 20:44:49 -07:00
pcmcia treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 247 2019-06-19 17:09:08 +02:00
perf perf intel-pt: Fix potential NULL pointer dereference found by the smatch tool 2019-07-09 10:13:28 -03:00
power platform-drivers-x86 for v5.3-1 2019-07-14 16:51:47 -07:00
scripts
spi treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 178 2019-05-30 11:29:19 -07:00
testing Merge branch 'akpm' (patches from Andrew) 2019-07-17 08:58:04 -07:00
thermal/tmon treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 89 2019-05-24 17:37:52 +02:00
time treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 282 2019-06-05 17:36:37 +02:00
usb treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 157 2019-05-30 11:26:37 -07:00
virtio treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 482 2019-06-19 17:09:52 +02:00
vm tools/vm/slabinfo: add sorting info to help menu 2019-07-12 11:05:46 -07:00
wmi treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 500 2019-06-19 17:09:55 +02:00
Makefile tools/power/x86: A tool to validate Intel Speed Select commands 2019-07-03 15:37:09 +03:00