From: Daniel Borkmann daniel@iogearbox.net
commit 5b9fbeb75b6a98955f628e205ac26689bcb1383e upstream.
Simon reported an issue with the current scalar32_min_max_or() implementation. That is, compared to the other 32 bit subreg tracking functions, the code in scalar32_min_max_or() stands out that it's using the 64 bit registers instead of 32 bit ones. This leads to bounds tracking issues, for example:
[...] 8: R0=map_value(id=0,off=0,ks=4,vs=48,imm=0) R10=fp0 fp-8=mmmmmmmm 8: (79) r1 = *(u64 *)(r0 +0) R0=map_value(id=0,off=0,ks=4,vs=48,imm=0) R10=fp0 fp-8=mmmmmmmm 9: R0=map_value(id=0,off=0,ks=4,vs=48,imm=0) R1_w=inv(id=0) R10=fp0 fp-8=mmmmmmmm 9: (b7) r0 = 1 10: R0_w=inv1 R1_w=inv(id=0) R10=fp0 fp-8=mmmmmmmm 10: (18) r2 = 0x600000002 12: R0_w=inv1 R1_w=inv(id=0) R2_w=inv25769803778 R10=fp0 fp-8=mmmmmmmm 12: (ad) if r1 < r2 goto pc+1 R0_w=inv1 R1_w=inv(id=0,umin_value=25769803778) R2_w=inv25769803778 R10=fp0 fp-8=mmmmmmmm 13: R0_w=inv1 R1_w=inv(id=0,umin_value=25769803778) R2_w=inv25769803778 R10=fp0 fp-8=mmmmmmmm 13: (95) exit 14: R0_w=inv1 R1_w=inv(id=0,umax_value=25769803777,var_off=(0x0; 0x7ffffffff)) R2_w=inv25769803778 R10=fp0 fp-8=mmmmmmmm 14: (25) if r1 > 0x0 goto pc+1 R0_w=inv1 R1_w=inv(id=0,umax_value=0,var_off=(0x0; 0x7fffffff),u32_max_value=2147483647) R2_w=inv25769803778 R10=fp0 fp-8=mmmmmmmm 15: R0_w=inv1 R1_w=inv(id=0,umax_value=0,var_off=(0x0; 0x7fffffff),u32_max_value=2147483647) R2_w=inv25769803778 R10=fp0 fp-8=mmmmmmmm 15: (95) exit 16: R0_w=inv1 R1_w=inv(id=0,umin_value=1,umax_value=25769803777,var_off=(0x0; 0x77fffffff),u32_max_value=2147483647) R2_w=inv25769803778 R10=fp0 fp-8=mmmmmmmm 16: (47) r1 |= 0 17: R0_w=inv1 R1_w=inv(id=0,umin_value=1,umax_value=32212254719,var_off=(0x1; 0x700000000),s32_max_value=1,u32_max_value=1) R2_w=inv25769803778 R10=fp0 fp-8=mmmmmmmm [...]
The bound tests on the map value force the upper unsigned bound to be 25769803777 in 64 bit (0b11000000000000000000000000000000001) and then lower one to be 1. By using OR they are truncated and thus result in the range [1,1] for the 32 bit reg tracker. This is incorrect given the only thing we know is that the value must be positive and thus 2147483647 (0b1111111111111111111111111111111) at max for the subregs. Fix it by using the {u,s}32_{min,max}_value vars instead. This also makes sense, for example, for the case where we update dst_reg->s32_{min,max}_value in the else branch we need to use the newly computed dst_reg->u32_{min,max}_value as we know that these are positive. Previously, in the else branch the 64 bit values of umin_value=1 and umax_value=32212254719 were used and latter got truncated to be 1 as upper bound there. After the fix the subreg range is now correct:
[...] 8: R0=map_value(id=0,off=0,ks=4,vs=48,imm=0) R10=fp0 fp-8=mmmmmmmm 8: (79) r1 = *(u64 *)(r0 +0) R0=map_value(id=0,off=0,ks=4,vs=48,imm=0) R10=fp0 fp-8=mmmmmmmm 9: R0=map_value(id=0,off=0,ks=4,vs=48,imm=0) R1_w=inv(id=0) R10=fp0 fp-8=mmmmmmmm 9: (b7) r0 = 1 10: R0_w=inv1 R1_w=inv(id=0) R10=fp0 fp-8=mmmmmmmm 10: (18) r2 = 0x600000002 12: R0_w=inv1 R1_w=inv(id=0) R2_w=inv25769803778 R10=fp0 fp-8=mmmmmmmm 12: (ad) if r1 < r2 goto pc+1 R0_w=inv1 R1_w=inv(id=0,umin_value=25769803778) R2_w=inv25769803778 R10=fp0 fp-8=mmmmmmmm 13: R0_w=inv1 R1_w=inv(id=0,umin_value=25769803778) R2_w=inv25769803778 R10=fp0 fp-8=mmmmmmmm 13: (95) exit 14: R0_w=inv1 R1_w=inv(id=0,umax_value=25769803777,var_off=(0x0; 0x7ffffffff)) R2_w=inv25769803778 R10=fp0 fp-8=mmmmmmmm 14: (25) if r1 > 0x0 goto pc+1 R0_w=inv1 R1_w=inv(id=0,umax_value=0,var_off=(0x0; 0x7fffffff),u32_max_value=2147483647) R2_w=inv25769803778 R10=fp0 fp-8=mmmmmmmm 15: R0_w=inv1 R1_w=inv(id=0,umax_value=0,var_off=(0x0; 0x7fffffff),u32_max_value=2147483647) R2_w=inv25769803778 R10=fp0 fp-8=mmmmmmmm 15: (95) exit 16: R0_w=inv1 R1_w=inv(id=0,umin_value=1,umax_value=25769803777,var_off=(0x0; 0x77fffffff),u32_max_value=2147483647) R2_w=inv25769803778 R10=fp0 fp-8=mmmmmmmm 16: (47) r1 |= 0 17: R0_w=inv1 R1_w=inv(id=0,umin_value=1,umax_value=32212254719,var_off=(0x0; 0x77fffffff),u32_max_value=2147483647) R2_w=inv25769803778 R10=fp0 fp-8=mmmmmmmm [...]
Fixes: 3f50f132d840 ("bpf: Verifier, do explicit ALU32 bounds tracking") Reported-by: Simon Scannell scannell.smn@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 | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-)
--- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -5490,8 +5490,8 @@ static void scalar32_min_max_or(struct b bool src_known = tnum_subreg_is_const(src_reg->var_off); bool dst_known = tnum_subreg_is_const(dst_reg->var_off); struct tnum var32_off = tnum_subreg(dst_reg->var_off); - s32 smin_val = src_reg->smin_value; - u32 umin_val = src_reg->umin_value; + s32 smin_val = src_reg->s32_min_value; + u32 umin_val = src_reg->u32_min_value;
/* Assuming scalar64_min_max_or will be called so it is safe * to skip updating register for known case. @@ -5514,8 +5514,8 @@ static void scalar32_min_max_or(struct b /* ORing two positives gives a positive, so safe to * cast result into s64. */ - dst_reg->s32_min_value = dst_reg->umin_value; - dst_reg->s32_max_value = dst_reg->umax_value; + dst_reg->s32_min_value = dst_reg->u32_min_value; + dst_reg->s32_max_value = dst_reg->u32_max_value; } }