commit 50fe7ebb6475711c15b3397467e6424e20026d94 upstream.

The current JIT clobbers the destination register for BPF_JSET BPF_X and BPF_K by using "and" and "or" instructions. This is fine when the destination register is a temporary loaded from a register stored on the stack but not otherwise.

This patch fixes the problem (for both BPF_K and BPF_X) by always loading the destination register into temporaries since BPF_JSET should not modify the destination register.

This bug may not be currently triggerable as BPF_REG_AX is the only register not stored on the stack and the verifier uses it in a limited way.

Fixes: 03f5781be2c7b ("bpf, x86_32: add eBPF JIT compiler for ia32") 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 Acked-by: Wang YanQing udknight@gmail.com Link: https://lore.kernel.org/bpf/20200422173630.8351-2-luke.r.nels@gmail.com Signed-off-by: Wang YanQing udknight@gmail.com --- arch/x86/net/bpf_jit_comp32.c | 20 ++++++++++++++++---- 1 file changed, 16 insertions(+), 4 deletions(-)

diff --git a/arch/x86/net/bpf_jit_comp32.c b/arch/x86/net/bpf_jit_comp32.c index 24d573b..7e7ca5d 100644 --- a/arch/x86/net/bpf_jit_comp32.c +++ b/arch/x86/net/bpf_jit_comp32.c @@ -1968,8 +1968,8 @@ static int do_jit(struct bpf_prog *bpf_prog, int *addrs, u8 *image, goto emit_cond_jmp_signed; } case BPF_JMP | BPF_JSET | BPF_X: { - u8 dreg_lo = dstk ? IA32_EAX : dst_lo; - u8 dreg_hi = dstk ? IA32_EDX : dst_hi; + u8 dreg_lo = IA32_EAX; + u8 dreg_hi = IA32_EDX; u8 sreg_lo = sstk ? IA32_ECX : src_lo; u8 sreg_hi = sstk ? IA32_EBX : src_hi;

@@ -1978,6 +1978,12 @@ static int do_jit(struct bpf_prog *bpf_prog, int *addrs, u8 *image, STACK_VAR(dst_lo)); EMIT3(0x8B, add_2reg(0x40, IA32_EBP, IA32_EDX), STACK_VAR(dst_hi)); + } else { + /* mov dreg_lo,dst_lo */ + EMIT2(0x89, add_2reg(0xC0, dreg_lo, dst_lo)); + /* mov dreg_hi,dst_hi */ + EMIT2(0x89, + add_2reg(0xC0, dreg_hi, dst_hi)); }

if (sstk) { @@ -1996,8 +2002,8 @@ static int do_jit(struct bpf_prog *bpf_prog, int *addrs, u8 *image, } case BPF_JMP | BPF_JSET | BPF_K: { u32 hi; - u8 dreg_lo = dstk ? IA32_EAX : dst_lo; - u8 dreg_hi = dstk ? IA32_EDX : dst_hi; + u8 dreg_lo = IA32_EAX; + u8 dreg_hi = IA32_EDX; u8 sreg_lo = IA32_ECX; u8 sreg_hi = IA32_EBX;

@@ -2006,6 +2012,12 @@ static int do_jit(struct bpf_prog *bpf_prog, int *addrs, u8 *image, STACK_VAR(dst_lo)); EMIT3(0x8B, add_2reg(0x40, IA32_EBP, IA32_EDX), STACK_VAR(dst_hi)); + } else { + /* mov dreg_lo,dst_lo */ + EMIT2(0x89, add_2reg(0xC0, dreg_lo, dst_lo)); + /* mov dreg_hi,dst_hi */ + EMIT2(0x89, + add_2reg(0xC0, dreg_hi, dst_hi)); } hi = imm32 & (1<<31) ? (u32)~0 : 0;