This is a note to let you know that I've just added the patch titled bpf, x86_32: Fix clobbering of dst for BPF_JSET to the 4.19-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: bpf-x86_32-fix-clobbering-of-dst-for-bpf_jset.patch and it can be found in the queue-4.19 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From 50fe7ebb6475711c15b3397467e6424e20026d94 Mon Sep 17 00:00:00 2001 From: Luke Nelson <lukenels@xxxxxxxxxxxxxxxxx> Date: Wed, 22 Apr 2020 10:36:30 -0700 Subject: bpf, x86_32: Fix clobbering of dst for BPF_JSET From: Luke Nelson <lukenels@xxxxxxxxxxxxxxxxx> 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@xxxxxxxxx> Signed-off-by: Luke Nelson <luke.r.nels@xxxxxxxxx> Signed-off-by: Alexei Starovoitov <ast@xxxxxxxxxx> Acked-by: Wang YanQing <udknight@xxxxxxxxx> Link: https://lore.kernel.org/bpf/20200422173630.8351-2-luke.r.nels@xxxxxxxxx Signed-off-by: Wang YanQing <udknight@xxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- arch/x86/net/bpf_jit_comp32.c | 20 ++++++++++++++++---- 1 file changed, 16 insertions(+), 4 deletions(-) --- a/arch/x86/net/bpf_jit_comp32.c +++ b/arch/x86/net/bpf_jit_comp32.c @@ -1970,8 +1970,8 @@ static int do_jit(struct bpf_prog *bpf_p 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; @@ -1980,6 +1980,12 @@ static int do_jit(struct bpf_prog *bpf_p 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) { @@ -1998,8 +2004,8 @@ static int do_jit(struct bpf_prog *bpf_p } 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; @@ -2008,6 +2014,12 @@ static int do_jit(struct bpf_prog *bpf_p 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; Patches currently in stable-queue which might be from lukenels@xxxxxxxxxxxxxxxxx are queue-4.19/bpf-x86_32-fix-incorrect-encoding-in-bpf_ldx-zero-extension.patch queue-4.19/bpf-x86-fix-encoding-for-lower-8-bit-registers-in-bp.patch queue-4.19/bpf-x86_32-fix-clobbering-of-dst-for-bpf_jset.patch