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Subject[tip: x86/urgent] objtool: Fix infinite loop in for_offset_range()
The following commit has been merged into the x86/urgent branch of tip:

Commit-ID: 53fb6e990d782ded62d7c76d566e107c03393b74
Gitweb: https://git.kernel.org/tip/53fb6e990d782ded62d7c76d566e107c03393b74
Author: Josh Poimboeuf <jpoimboe@redhat.com>
AuthorDate: Sat, 25 Apr 2020 14:19:01 -05:00
Committer: Ingo Molnar <mingo@kernel.org>
CommitterDate: Sun, 26 Apr 2020 09:28:14 +02:00

objtool: Fix infinite loop in for_offset_range()

Randy reported that objtool got stuck in an infinite loop when
processing drivers/i2c/busses/i2c-parport.o. It was caused by the
following code:

00000000000001fd <line_set>:
1fd: 48 b8 00 00 00 00 00 movabs $0x0,%rax
204: 00 00 00
1ff: R_X86_64_64 .rodata-0x8
207: 41 55 push %r13
209: 41 89 f5 mov %esi,%r13d
20c: 41 54 push %r12
20e: 49 89 fc mov %rdi,%r12
211: 55 push %rbp
212: 48 89 d5 mov %rdx,%rbp
215: 53 push %rbx
216: 0f b6 5a 01 movzbl 0x1(%rdx),%ebx
21a: 48 8d 34 dd 00 00 00 lea 0x0(,%rbx,8),%rsi
221: 00
21e: R_X86_64_32S .rodata
222: 48 89 f1 mov %rsi,%rcx
225: 48 29 c1 sub %rax,%rcx

find_jump_table() saw the .rodata reference and tried to find a jump
table associated with it (though there wasn't one). The -0x8 rela
addend is unusual. It caused find_jump_table() to send a negative
table_offset (unsigned 0xfffffffffffffff8) to find_rela_by_dest().

The negative offset should have been harmless, but it actually threw
for_offset_range() for a loop... literally. When the mask value got
incremented past the end value, it also wrapped to zero, causing the
loop exit condition to remain true forever.

Prevent this scenario from happening by ensuring the incremented value
is always >= the starting value.

Fixes: 74b873e49d92 ("objtool: Optimize find_rela_by_dest_range()")
Reported-by: Randy Dunlap <rdunlap@infradead.org>
Tested-by: Randy Dunlap <rdunlap@infradead.org>
Acked-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Julien Thierry <jthierry@redhat.com>
Cc: Miroslav Benes <mbenes@suse.cz>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/02b719674b031800b61e33c30b2e823183627c19.1587842122.git.jpoimboe@redhat.com
---
tools/objtool/elf.h | 7 ++++---
1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/tools/objtool/elf.h b/tools/objtool/elf.h
index ebbb10c..c227a2e 100644
--- a/tools/objtool/elf.h
+++ b/tools/objtool/elf.h
@@ -87,9 +87,10 @@ struct elf {
#define OFFSET_STRIDE (1UL << OFFSET_STRIDE_BITS)
#define OFFSET_STRIDE_MASK (~(OFFSET_STRIDE - 1))

-#define for_offset_range(_offset, _start, _end) \
- for (_offset = ((_start) & OFFSET_STRIDE_MASK); \
- _offset <= ((_end) & OFFSET_STRIDE_MASK); \
+#define for_offset_range(_offset, _start, _end) \
+ for (_offset = ((_start) & OFFSET_STRIDE_MASK); \
+ _offset >= ((_start) & OFFSET_STRIDE_MASK) && \
+ _offset <= ((_end) & OFFSET_STRIDE_MASK); \
_offset += OFFSET_STRIDE)

static inline u32 sec_offset_hash(struct section *sec, unsigned long offset)
\
 
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