From: Daniel Borkmann daniel@iogearbox.net
commit 3cf2b61eb06765e27fec6799292d9fb46d0b7e60 upstream.
For the case where both s32_{min,max}_value bounds are positive, the __reg_assign_32_into_64() directly propagates them to their 64 bit counterparts, otherwise it pessimises them into [0,u32_max] universe and tries to refine them later on by learning through the tnum as per comment in mentioned function. However, that does not always happen, for example, in mov32 operation we call zext_32_to_64(dst_reg) which invokes the __reg_assign_32_into_64() as is without subsequent bounds update as elsewhere thus no refinement based on tnum takes place.
Thus, not calling into the __update_reg_bounds() / __reg_deduce_bounds() / __reg_bound_offset() triplet as we do, for example, in case of ALU ops via adjust_scalar_min_max_vals(), will lead to more pessimistic bounds when dumping the full register state:
Before fix:
0: (b4) w0 = -1 1: R0_w=invP4294967295 (id=0,imm=ffffffff, smin_value=4294967295,smax_value=4294967295, umin_value=4294967295,umax_value=4294967295, var_off=(0xffffffff; 0x0), s32_min_value=-1,s32_max_value=-1, u32_min_value=-1,u32_max_value=-1)
1: (bc) w0 = w0 2: R0_w=invP4294967295 (id=0,imm=ffffffff, smin_value=0,smax_value=4294967295, umin_value=4294967295,umax_value=4294967295, var_off=(0xffffffff; 0x0), s32_min_value=-1,s32_max_value=-1, u32_min_value=-1,u32_max_value=-1)
Technically, the smin_value=0 and smax_value=4294967295 bounds are not incorrect, but given the register is still a constant, they break assumptions about const scalars that smin_value == smax_value and umin_value == umax_value.
After fix:
0: (b4) w0 = -1 1: R0_w=invP4294967295 (id=0,imm=ffffffff, smin_value=4294967295,smax_value=4294967295, umin_value=4294967295,umax_value=4294967295, var_off=(0xffffffff; 0x0), s32_min_value=-1,s32_max_value=-1, u32_min_value=-1,u32_max_value=-1)
1: (bc) w0 = w0 2: R0_w=invP4294967295 (id=0,imm=ffffffff, smin_value=4294967295,smax_value=4294967295, umin_value=4294967295,umax_value=4294967295, var_off=(0xffffffff; 0x0), s32_min_value=-1,s32_max_value=-1, u32_min_value=-1,u32_max_value=-1)
Without the smin_value == smax_value and umin_value == umax_value invariant being intact for const scalars, it is possible to leak out kernel pointers from unprivileged user space if the latter is enabled. For example, when such registers are involved in pointer arithmtics, then adjust_ptr_min_max_vals() will taint the destination register into an unknown scalar, and the latter can be exported and stored e.g. into a BPF map value.
Fixes: 3f50f132d840 ("bpf: Verifier, do explicit ALU32 bounds tracking") Reported-by: Kuee K1r0a liulin063@gmail.com Signed-off-by: Daniel Borkmann daniel@iogearbox.net Reviewed-by: John Fastabend john.fastabend@gmail.com Acked-by: Alexei Starovoitov ast@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- kernel/bpf/verifier.c | 4 ++++ 1 file changed, 4 insertions(+)
--- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -8120,6 +8120,10 @@ static int check_alu_op(struct bpf_verif insn->dst_reg); } zext_32_to_64(dst_reg); + + __update_reg_bounds(dst_reg); + __reg_deduce_bounds(dst_reg); + __reg_bound_offset(dst_reg); } } else { /* case: R = imm