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ced185824c
Fix the case where the dst register maps to %rax as otherwise this produces an incorrect mapping with the implementation in981f94c3e9("bpf: Add bitwise atomic instructions") as %rax is clobbered given it's part of the cmpxchg as operand. The issue is similar tob29dd96b90("bpf, x86: Fix BPF_FETCH atomic and/or/ xor with r0 as src") just that the case of dst register was missed. Before, dst=r0 (%rax) src=r2 (%rsi): [...] c5: mov %rax,%r10 c8: mov 0x0(%rax),%rax <---+ (broken) cc: mov %rax,%r11 | cf: and %rsi,%r11 | d2: lock cmpxchg %r11,0x0(%rax) <---+ d8: jne 0x00000000000000c8 | da: mov %rax,%rsi | dd: mov %r10,%rax | [...] | | After, dst=r0 (%rax) src=r2 (%rsi): | | [...] | da: mov %rax,%r10 | dd: mov 0x0(%r10),%rax <---+ (fixed) e1: mov %rax,%r11 | e4: and %rsi,%r11 | e7: lock cmpxchg %r11,0x0(%r10) <---+ ed: jne 0x00000000000000dd ef: mov %rax,%rsi f2: mov %r10,%rax [...] The remaining combinations were fine as-is though: After, dst=r9 (%r15) src=r0 (%rax): [...] dc: mov %rax,%r10 df: mov 0x0(%r15),%rax e3: mov %rax,%r11 e6: and %r10,%r11 e9: lock cmpxchg %r11,0x0(%r15) ef: jne 0x00000000000000df _ f1: mov %rax,%r10 | (unneeded, but f4: mov %r10,%rax _| not a problem) [...] After, dst=r9 (%r15) src=r4 (%rcx): [...] de: mov %rax,%r10 e1: mov 0x0(%r15),%rax e5: mov %rax,%r11 e8: and %rcx,%r11 eb: lock cmpxchg %r11,0x0(%r15) f1: jne 0x00000000000000e1 f3: mov %rax,%rcx f6: mov %r10,%rax [...] The case of dst == src register is rejected by the verifier and therefore not supported, but x86 JIT also handles this case just fine. After, dst=r0 (%rax) src=r0 (%rax): [...] eb: mov %rax,%r10 ee: mov 0x0(%r10),%rax f2: mov %rax,%r11 f5: and %r10,%r11 f8: lock cmpxchg %r11,0x0(%r10) fe: jne 0x00000000000000ee 100: mov %rax,%r10 103: mov %r10,%rax [...] Fixes:981f94c3e9("bpf: Add bitwise atomic instructions") Reported-by: Johan Almbladh <johan.almbladh@anyfinetworks.com> Signed-off-by: Johan Almbladh <johan.almbladh@anyfinetworks.com> Co-developed-by: Daniel Borkmann <daniel@iogearbox.net> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Reviewed-by: Brendan Jackman <jackmanb@google.com> Acked-by: Alexei Starovoitov <ast@kernel.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.