From: Daniel Borkmann daniel@iogearbox.net
[ Upstream commit 10bf4e83167cc68595b85fd73bb91e8f2c086e36 ]
Similarly as b02709587ea3 ("bpf: Fix propagation of 32-bit signed bounds from 64-bit bounds."), we also need to fix the propagation of 32 bit unsigned bounds from 64 bit counterparts. That is, really only set the u32_{min,max}_value when /both/ {umin,umax}_value safely fit in 32 bit space. For example, the register with a umin_value == 1 does /not/ imply that u32_min_value is also equal to 1, since umax_value could be much larger than 32 bit subregister can hold, and thus u32_min_value is in the interval [0,1] instead.
Before fix, invalid tracking result of R2_w=inv1:
[...] 5: R0_w=inv1337 R1=ctx(id=0,off=0,imm=0) R2_w=inv(id=0) R10=fp0 5: (35) if r2 >= 0x1 goto pc+1 [...] // goto path 7: R0=inv1337 R1=ctx(id=0,off=0,imm=0) R2=inv(id=0,umin_value=1) R10=fp0 7: (b6) if w2 <= 0x1 goto pc+1 [...] // goto path 9: R0=inv1337 R1=ctx(id=0,off=0,imm=0) R2=inv(id=0,smin_value=-9223372036854775807,smax_value=9223372032559808513,umin_value=1,umax_value=18446744069414584321,var_off=(0x1; 0xffffffff00000000),s32_min_value=1,s32_max_value=1,u32_max_value=1) R10=fp0 9: (bc) w2 = w2 10: R0=inv1337 R1=ctx(id=0,off=0,imm=0) R2_w=inv1 R10=fp0 [...]
After fix, correct tracking result of R2_w=inv(id=0,umax_value=1,var_off=(0x0; 0x1)):
[...] 5: R0_w=inv1337 R1=ctx(id=0,off=0,imm=0) R2_w=inv(id=0) R10=fp0 5: (35) if r2 >= 0x1 goto pc+1 [...] // goto path 7: R0=inv1337 R1=ctx(id=0,off=0,imm=0) R2=inv(id=0,umin_value=1) R10=fp0 7: (b6) if w2 <= 0x1 goto pc+1 [...] // goto path 9: R0=inv1337 R1=ctx(id=0,off=0,imm=0) R2=inv(id=0,smax_value=9223372032559808513,umax_value=18446744069414584321,var_off=(0x0; 0xffffffff00000001),s32_min_value=0,s32_max_value=1,u32_max_value=1) R10=fp0 9: (bc) w2 = w2 10: R0=inv1337 R1=ctx(id=0,off=0,imm=0) R2_w=inv(id=0,umax_value=1,var_off=(0x0; 0x1)) R10=fp0 [...]
Thus, same issue as in b02709587ea3 holds for unsigned subregister tracking. Also, align __reg64_bound_u32() similarly to __reg64_bound_s32() as done in b02709587ea3 to make them uniform again.
Fixes: 3f50f132d840 ("bpf: Verifier, do explicit ALU32 bounds tracking") Reported-by: Manfred Paul (@_manfp) 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: Sasha Levin sashal@kernel.org --- kernel/bpf/verifier.c | 8 +++----- tools/testing/selftests/bpf/verifier/array_access.c | 2 +- 2 files changed, 4 insertions(+), 6 deletions(-)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index a2ed7a7e27e2..42ec080b0ced 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -1362,9 +1362,7 @@ static bool __reg64_bound_s32(s64 a)
static bool __reg64_bound_u32(u64 a) { - if (a > U32_MIN && a < U32_MAX) - return true; - return false; + return a > U32_MIN && a < U32_MAX; }
static void __reg_combine_64_into_32(struct bpf_reg_state *reg) @@ -1375,10 +1373,10 @@ static void __reg_combine_64_into_32(struct bpf_reg_state *reg) reg->s32_min_value = (s32)reg->smin_value; reg->s32_max_value = (s32)reg->smax_value; } - if (__reg64_bound_u32(reg->umin_value)) + if (__reg64_bound_u32(reg->umin_value) && __reg64_bound_u32(reg->umax_value)) { reg->u32_min_value = (u32)reg->umin_value; - if (__reg64_bound_u32(reg->umax_value)) reg->u32_max_value = (u32)reg->umax_value; + }
/* Intersecting with the old var_off might have improved our bounds * slightly. e.g. if umax was 0x7f...f and var_off was (0; 0xf...fc), diff --git a/tools/testing/selftests/bpf/verifier/array_access.c b/tools/testing/selftests/bpf/verifier/array_access.c index 1b138cd2b187..1b1c798e9248 100644 --- a/tools/testing/selftests/bpf/verifier/array_access.c +++ b/tools/testing/selftests/bpf/verifier/array_access.c @@ -186,7 +186,7 @@ }, .fixup_map_hash_48b = { 3 }, .errstr_unpriv = "R0 leaks addr", - .errstr = "invalid access to map value, value_size=48 off=44 size=8", + .errstr = "R0 unbounded memory access", .result_unpriv = REJECT, .result = REJECT, .flags = F_NEEDS_EFFICIENT_UNALIGNED_ACCESS,