Commit 50fe7ebb authored by Luke Nelson's avatar Luke Nelson Committed by Alexei Starovoitov
Browse files

bpf, x86_32: Fix clobbering of dst for BPF_JSET 



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: 03f5781b ("bpf, x86_32: add eBPF JIT compiler for ia32")
Signed-off-by: default avatarXi Wang <xi.wang@gmail.com>
Signed-off-by: default avatarLuke Nelson <luke.r.nels@gmail.com>
Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
Acked-by: default avatarWang YanQing <udknight@gmail.com>
Link: https://lore.kernel.org/bpf/20200422173630.8351-2-luke.r.nels@gmail.com
parent 5fa9a98f

arch/x86/net/bpf_jit_comp32.c

+18 −4
Original line number Diff line number Diff line
@@ -2015,8 +2015,8 @@ static int do_jit(struct bpf_prog *bpf_prog, int *addrs, u8 *image, 
		case BPF_JMP | BPF_JSET | BPF_X:

		case BPF_JMP32 | BPF_JSET | BPF_X: {

			bool is_jmp64 = BPF_CLASS(insn->code) == BPF_JMP;

			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;
@@ -2028,6 +2028,13 @@ static int do_jit(struct bpf_prog *bpf_prog, int *addrs, u8 *image, 
					      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));

				if (is_jmp64)

					/* mov dreg_hi,dst_hi */

					EMIT2(0x89,

					      add_2reg(0xC0, dreg_hi, dst_hi));

			}



			if (sstk) {
@@ -2052,8 +2059,8 @@ static int do_jit(struct bpf_prog *bpf_prog, int *addrs, u8 *image, 
		case BPF_JMP | BPF_JSET | BPF_K:

		case BPF_JMP32 | BPF_JSET | BPF_K: {

			bool is_jmp64 = BPF_CLASS(insn->code) == BPF_JMP;

			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;

			u32 hi;
@@ -2066,6 +2073,13 @@ static int do_jit(struct bpf_prog *bpf_prog, int *addrs, u8 *image, 
					      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));

				if (is_jmp64)

					/* mov dreg_hi,dst_hi */

					EMIT2(0x89,

					      add_2reg(0xC0, dreg_hi, dst_hi));

			}



			/* mov ecx,imm32 */

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