Luke Nelson aee194b14d bpf, x86: Fix encoding for lower 8-bit registers in BPF_STX BPF_B ... This patch fixes an encoding bug in emit_stx for BPF_B when the source register is BPF_REG_FP. The current implementation for BPF_STX BPF_B in emit_stx saves one REX byte when the operands can be encoded using Mod-R/M alone. The lower 8 bits of registers %rax, %rbx, %rcx, and %rdx can be accessed without using a REX prefix via %al, %bl, %cl, and %dl, respectively. Other registers, (e.g., %rsi, %rdi, %rbp, %rsp) require a REX prefix to use their 8-bit equivalents (%sil, %dil, %bpl, %spl). The current code checks if the source for BPF_STX BPF_B is BPF_REG_1 or BPF_REG_2 (which map to %rdi and %rsi), in which case it emits the required REX prefix. However, it misses the case when the source is BPF_REG_FP (mapped to %rbp). The result is that BPF_STX BPF_B with BPF_REG_FP as the source operand will read from register %ch instead of the correct %bpl. This patch fixes the problem by fixing and refactoring the check on which registers need the extra REX byte. Since no BPF registers map to %rsp, there is no need to handle %spl. Fixes: 622582786c ("net: filter: x86: internal BPF JIT") Signed-off-by: Xi Wang <xi.wang@gmail.com> Signed-off-by: Luke Nelson <luke.r.nels@gmail.com> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Link: https://lore.kernel.org/bpf/20200418232655.23870-1-luke.r.nels@gmail.com		2020-04-20 19:25:30 -07:00
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bpf_jit_comp32.c	bpf, x32: Fix bug with JMP32 JSET BPF_X checking upper bits	2020-03-06 14:17:39 +01:00
bpf_jit_comp.c	bpf, x86: Fix encoding for lower 8-bit registers in BPF_STX BPF_B	2020-04-20 19:25:30 -07:00
Makefile	treewide: Add SPDX license identifier - Makefile/Kconfig	2019-05-21 10:50:46 +02:00