user/sven/linux.git/kernel/bpf, branch v4.11.11

bpf: adjust verifier heuristics

2017-06-07T10:10:05Z

[ Upstream commit 3c2ce60bdd3d57051bf85615deec04a694473840 ] Current limits with regards to processing program paths do not really reflect today's needs anymore due to programs becoming more complex and verifier smarter, keeping track of more data such as const ALU operations, alignment tracking, spilling of PTR_TO_MAP_VALUE_ADJ registers, and other features allowing for smarter matching of what LLVM generates. This also comes with the side-effect that we result in fewer opportunities to prune search states and thus often need to do more work to prove safety than in the past due to different register states and stack layout where we mismatch. Generally, it's quite hard to determine what caused a sudden increase in complexity, it could be caused by something as trivial as a single branch somewhere at the beginning of the program where LLVM assigned a stack slot that is marked differently throughout other branches and thus causing a mismatch, where verifier then needs to prove safety for the whole rest of the program. Subsequently, programs with even less than half the insn size limit can get rejected. We noticed that while some programs load fine under pre 4.11, they get rejected due to hitting limits on more recent kernels. We saw that in the vast majority of cases (90+%) pruning failed due to register mismatches. In case of stack mismatches, majority of cases failed due to different stack slot types (invalid, spill, misc) rather than differences in spilled registers. This patch makes pruning more aggressive by also adding markers that sit at conditional jumps as well. Currently, we only mark jump targets for pruning. For example in direct packet access, these are usually error paths where we bail out. We found that adding these markers, it can reduce number of processed insns by up to 30%. Another option is to ignore reg->id in probing PTR_TO_MAP_VALUE_OR_NULL registers, which can help pruning slightly as well by up to 7% observed complexity reduction as stand-alone. Meaning, if a previous path with register type PTR_TO_MAP_VALUE_OR_NULL for map X was found to be safe, then in the current state a PTR_TO_MAP_VALUE_OR_NULL register for the same map X must be safe as well. Last but not least the patch also adds a scheduling point and bumps the current limit for instructions to be processed to a more adequate value. Signed-off-by: Daniel Borkmann Acked-by: Alexei Starovoitov Signed-off-by: David S. Miller Signed-off-by: Greg Kroah-Hartman

bpf: fix wrong exposure of map_flags into fdinfo for lpm

2017-06-07T10:10:05Z

[ Upstream commit a316338cb71a3260201490e615f2f6d5c0d8fb2c ] trie_alloc() always needs to have BPF_F_NO_PREALLOC passed in via attr->map_flags, since it does not support preallocation yet. We check the flag, but we never copy the flag into trie->map.map_flags, which is later on exposed into fdinfo and used by loaders such as iproute2. Latter uses this in bpf_map_selfcheck_pinned() to test whether a pinned map has the same spec as the one from the BPF obj file and if not, bails out, which is currently the case for lpm since it exposes always 0 as flags. Also copy over flags in array_map_alloc() and stack_map_alloc(). They always have to be 0 right now, but we should make sure to not miss to copy them over at a later point in time when we add actual flags for them to use. Fixes: b95a5c4db09b ("bpf: add a longest prefix match trie map implementation") Reported-by: Jarno Rajahalme Signed-off-by: Daniel Borkmann Acked-by: Alexei Starovoitov Signed-off-by: David S. Miller Signed-off-by: Greg Kroah-Hartman

bpf: don't let ldimm64 leak map addresses on unprivileged

2017-05-14T12:06:02Z

[ Upstream commit 0d0e57697f162da4aa218b5feafe614fb666db07 ] The patch fixes two things at once: 1) It checks the env->allow_ptr_leaks and only prints the map address to the log if we have the privileges to do so, otherwise it just dumps 0 as we would when kptr_restrict is enabled on %pK. Given the latter is off by default and not every distro sets it, I don't want to rely on this, hence the 0 by default for unprivileged. 2) Printing of ldimm64 in the verifier log is currently broken in that we don't print the full immediate, but only the 32 bit part of the first insn part for ldimm64. Thus, fix this up as well; it's okay to access, since we verified all ldimm64 earlier already (including just constants) through replace_map_fd_with_map_ptr(). Fixes: 1be7f75d1668 ("bpf: enable non-root eBPF programs") Fixes: cbd357008604 ("bpf: verifier (add ability to receive verification log)") Reported-by: Jann Horn Signed-off-by: Daniel Borkmann Acked-by: Alexei Starovoitov Signed-off-by: David S. Miller Signed-off-by: Greg Kroah-Hartman

bpf: enhance verifier to understand stack pointer arithmetic

2017-05-14T12:06:01Z

[ Upstream commit 332270fdc8b6fba07d059a9ad44df9e1a2ad4529 ] llvm 4.0 and above generates the code like below: .... 440: (b7) r1 = 15 441: (05) goto pc+73 515: (79) r6 = *(u64 *)(r10 -152) 516: (bf) r7 = r10 517: (07) r7 += -112 518: (bf) r2 = r7 519: (0f) r2 += r1 520: (71) r1 = *(u8 *)(r8 +0) 521: (73) *(u8 *)(r2 +45) = r1 .... and the verifier complains "R2 invalid mem access 'inv'" for insn #521. This is because verifier marks register r2 as unknown value after #519 where r2 is a stack pointer and r1 holds a constant value. Teach verifier to recognize "stack_ptr + imm" and "stack_ptr + reg with const val" as valid stack_ptr with new offset. Signed-off-by: Yonghong Song Acked-by: Martin KaFai Lau Acked-by: Daniel Borkmann Signed-off-by: Alexei Starovoitov Signed-off-by: David S. Miller Signed-off-by: Greg Kroah-Hartman

bpf: fix checking xdp_adjust_head on tail calls

2017-04-17T19:51:57Z

Commit 17bedab27231 ("bpf: xdp: Allow head adjustment in XDP prog") added the xdp_adjust_head bit to the BPF prog in order to tell drivers that the program that is to be attached requires support for the XDP bpf_xdp_adjust_head() helper such that drivers not supporting this helper can reject the program. There are also drivers that do support the helper, but need to check for xdp_adjust_head bit in order to move packet metadata prepended by the firmware away for making headroom. For these cases, the current check for xdp_adjust_head bit is insufficient since there can be cases where the program itself does not use the bpf_xdp_adjust_head() helper, but tail calls into another program that uses bpf_xdp_adjust_head(). As such, the xdp_adjust_head bit is still set to 0. Since the first program has no control over which program it calls into, we need to assume that bpf_xdp_adjust_head() helper is used upon tail calls. Thus, for the very same reasons in cb_access, set the xdp_adjust_head bit to 1 when the main program uses tail calls. Fixes: 17bedab27231 ("bpf: xdp: Allow head adjustment in XDP prog") Signed-off-by: Daniel Borkmann Acked-by: Alexei Starovoitov Cc: Martin KaFai Lau Signed-off-by: David S. Miller

bpf: fix cb access in socket filter programs on tail calls

2017-04-17T19:51:57Z

Commit ff936a04e5f2 ("bpf: fix cb access in socket filter programs") added a fix for socket filter programs such that in i) AF_PACKET the 20 bytes of skb->cb[] area gets zeroed before use in order to not leak data, and ii) socket filter programs attached to TCP/UDP sockets need to save/restore these 20 bytes since they are also used by protocol layers at that time. The problem is that bpf_prog_run_save_cb() and bpf_prog_run_clear_cb() only look at the actual attached program to determine whether to zero or save/restore the skb->cb[] parts. There can be cases where the actual attached program does not access the skb->cb[], but the program tail calls into another program which does access this area. In such a case, the zero or save/restore is currently not performed. Since the programs we tail call into are unknown at verification time and can dynamically change, we need to assume that whenever the attached program performs a tail call, that later programs could access the skb->cb[], and therefore we need to always set cb_access to 1. Fixes: ff936a04e5f2 ("bpf: fix cb access in socket filter programs") Signed-off-by: Daniel Borkmann Acked-by: Alexei Starovoitov Signed-off-by: David S. Miller

bpf: reference may_access_skb() from __bpf_prog_run()

2017-04-11T14:54:27Z

It took me quite some time to figure out how this was linked, so in order to save the next person the effort of finding it add a comment in __bpf_prog_run() that indicates what exactly determines that a program can access the ctx == skb. Signed-off-by: Johannes Berg Acked-by: Daniel Borkmann Signed-off-by: David S. Miller

bpf, verifier: fix rejection of unaligned access checks for map_value_adj

2017-04-01T19:36:37Z

Currently, the verifier doesn't reject unaligned access for map_value_adj register types. Commit 484611357c19 ("bpf: allow access into map value arrays") added logic to check_ptr_alignment() extending it from PTR_TO_PACKET to also PTR_TO_MAP_VALUE_ADJ, but for PTR_TO_MAP_VALUE_ADJ no enforcement is in place, because reg->id for PTR_TO_MAP_VALUE_ADJ reg types is never non-zero, meaning, we can cause BPF_H/_W/_DW-based unaligned access for architectures not supporting efficient unaligned access, and thus worst case could raise exceptions on some archs that are unable to correct the unaligned access or perform a different memory access to the actual requested one and such. i) Unaligned load with !CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS on r0 (map_value_adj): 0: (bf) r2 = r10 1: (07) r2 += -8 2: (7a) *(u64 *)(r2 +0) = 0 3: (18) r1 = 0x42533a00 5: (85) call bpf_map_lookup_elem#1 6: (15) if r0 == 0x0 goto pc+11 R0=map_value(ks=8,vs=48,id=0),min_value=0,max_value=0 R10=fp 7: (61) r1 = *(u32 *)(r0 +0) 8: (35) if r1 >= 0xb goto pc+9 R0=map_value(ks=8,vs=48,id=0),min_value=0,max_value=0 R1=inv,min_value=0,max_value=10 R10=fp 9: (07) r0 += 3 10: (79) r7 = *(u64 *)(r0 +0) R0=map_value_adj(ks=8,vs=48,id=0),min_value=3,max_value=3 R1=inv,min_value=0,max_value=10 R10=fp 11: (79) r7 = *(u64 *)(r0 +2) R0=map_value_adj(ks=8,vs=48,id=0),min_value=3,max_value=3 R1=inv,min_value=0,max_value=10 R7=inv R10=fp [...] ii) Unaligned store with !CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS on r0 (map_value_adj): 0: (bf) r2 = r10 1: (07) r2 += -8 2: (7a) *(u64 *)(r2 +0) = 0 3: (18) r1 = 0x4df16a00 5: (85) call bpf_map_lookup_elem#1 6: (15) if r0 == 0x0 goto pc+19 R0=map_value(ks=8,vs=48,id=0),min_value=0,max_value=0 R10=fp 7: (07) r0 += 3 8: (7a) *(u64 *)(r0 +0) = 42 R0=map_value_adj(ks=8,vs=48,id=0),min_value=3,max_value=3 R10=fp 9: (7a) *(u64 *)(r0 +2) = 43 R0=map_value_adj(ks=8,vs=48,id=0),min_value=3,max_value=3 R10=fp 10: (7a) *(u64 *)(r0 -2) = 44 R0=map_value_adj(ks=8,vs=48,id=0),min_value=3,max_value=3 R10=fp [...] For the PTR_TO_PACKET type, reg->id is initially zero when skb->data was fetched, it later receives a reg->id from env->id_gen generator once another register with UNKNOWN_VALUE type was added to it via check_packet_ptr_add(). The purpose of this reg->id is twofold: i) it is used in find_good_pkt_pointers() for setting the allowed access range for regs with PTR_TO_PACKET of same id once verifier matched on data/data_end tests, and ii) for check_ptr_alignment() to determine that when not having efficient unaligned access and register with UNKNOWN_VALUE was added to PTR_TO_PACKET, that we're only allowed to access the content bytewise due to unknown unalignment. reg->id was never intended for PTR_TO_MAP_VALUE{,_ADJ} types and thus is always zero, the only marking is in PTR_TO_MAP_VALUE_OR_NULL that was added after 484611357c19 via 57a09bf0a416 ("bpf: Detect identical PTR_TO_MAP_VALUE_OR_NULL registers"). Above tests will fail for non-root environment due to prohibited pointer arithmetic. The fix splits register-type specific checks into their own helper instead of keeping them combined, so we don't run into a similar issue in future once we extend check_ptr_alignment() further and forget to add reg->type checks for some of the checks. Fixes: 484611357c19 ("bpf: allow access into map value arrays") Signed-off-by: Daniel Borkmann Reviewed-by: Josef Bacik Acked-by: Alexei Starovoitov Signed-off-by: David S. Miller

bpf, verifier: fix alu ops against map_value{, _adj} register types

2017-04-01T19:36:37Z

While looking into map_value_adj, I noticed that alu operations directly on the map_value() resp. map_value_adj() register (any alu operation on a map_value() register will turn it into a map_value_adj() typed register) are not sufficiently protected against some of the operations. Two non-exhaustive examples are provided that the verifier needs to reject: i) BPF_AND on r0 (map_value_adj): 0: (bf) r2 = r10 1: (07) r2 += -8 2: (7a) *(u64 *)(r2 +0) = 0 3: (18) r1 = 0xbf842a00 5: (85) call bpf_map_lookup_elem#1 6: (15) if r0 == 0x0 goto pc+2 R0=map_value(ks=8,vs=48,id=0),min_value=0,max_value=0 R10=fp 7: (57) r0 &= 8 8: (7a) *(u64 *)(r0 +0) = 22 R0=map_value_adj(ks=8,vs=48,id=0),min_value=0,max_value=8 R10=fp 9: (95) exit from 6 to 9: R0=inv,min_value=0,max_value=0 R10=fp 9: (95) exit processed 10 insns ii) BPF_ADD in 32 bit mode on r0 (map_value_adj): 0: (bf) r2 = r10 1: (07) r2 += -8 2: (7a) *(u64 *)(r2 +0) = 0 3: (18) r1 = 0xc24eee00 5: (85) call bpf_map_lookup_elem#1 6: (15) if r0 == 0x0 goto pc+2 R0=map_value(ks=8,vs=48,id=0),min_value=0,max_value=0 R10=fp 7: (04) (u32) r0 += (u32) 0 8: (7a) *(u64 *)(r0 +0) = 22 R0=map_value_adj(ks=8,vs=48,id=0),min_value=0,max_value=0 R10=fp 9: (95) exit from 6 to 9: R0=inv,min_value=0,max_value=0 R10=fp 9: (95) exit processed 10 insns Issue is, while min_value / max_value boundaries for the access are adjusted appropriately, we change the pointer value in a way that cannot be sufficiently tracked anymore from its origin. Operations like BPF_{AND,OR,DIV,MUL,etc} on a destination register that is PTR_TO_MAP_VALUE{,_ADJ} was probably unintended, in fact, all the test cases coming with 484611357c19 ("bpf: allow access into map value arrays") perform BPF_ADD only on the destination register that is PTR_TO_MAP_VALUE_ADJ. Only for UNKNOWN_VALUE register types such operations make sense, f.e. with unknown memory content fetched initially from a constant offset from the map value memory into a register. That register is then later tested against lower / upper bounds, so that the verifier can then do the tracking of min_value / max_value, and properly check once that UNKNOWN_VALUE register is added to the destination register with type PTR_TO_MAP_VALUE{,_ADJ}. This is also what the original use-case is solving. Note, tracking on what is being added is done through adjust_reg_min_max_vals() and later access to the map value enforced with these boundaries and the given offset from the insn through check_map_access_adj(). Tests will fail for non-root environment due to prohibited pointer arithmetic, in particular in check_alu_op(), we bail out on the is_pointer_value() check on the dst_reg (which is false in root case as we allow for pointer arithmetic via env->allow_ptr_leaks). Similarly to PTR_TO_PACKET, one way to fix it is to restrict the allowed operations on PTR_TO_MAP_VALUE{,_ADJ} registers to 64 bit mode BPF_ADD. The test_verifier suite runs fine after the patch and it also rejects mentioned test cases. Fixes: 484611357c19 ("bpf: allow access into map value arrays") Signed-off-by: Daniel Borkmann Reviewed-by: Josef Bacik Acked-by: Alexei Starovoitov Signed-off-by: David S. Miller

bpf: improve verifier packet range checks

2017-03-25T03:51:28Z

llvm can optimize the 'if (ptr > data_end)' checks to be in the order slightly different than the original C code which will confuse verifier. Like: if (ptr + 16 > data_end) return TC_ACT_SHOT; // may be followed by if (ptr + 14 > data_end) return TC_ACT_SHOT; while llvm can see that 'ptr' is valid for all 16 bytes, the verifier could not. Fix verifier logic to account for such case and add a test. Reported-by: Huapeng Zhou Fixes: 969bf05eb3ce ("bpf: direct packet access") Signed-off-by: Alexei Starovoitov Acked-by: Daniel Borkmann Acked-by: Martin KaFai Lau Signed-off-by: David S. Miller