linux/kernel/bpf/core.c, branch v5.15

bpf: Fix potential race in tail call compatibility check

2021-10-26T19:37:28Z

Lorenzo noticed that the code testing for program type compatibility of tail call maps is potentially racy in that two threads could encounter a map with an unset type simultaneously and both return true even though they are inserting incompatible programs. The race window is quite small, but artificially enlarging it by adding a usleep_range() inside the check in bpf_prog_array_compatible() makes it trivial to trigger from userspace with a program that does, essentially: map_fd = bpf_create_map(BPF_MAP_TYPE_PROG_ARRAY, 4, 4, 2, 0); pid = fork(); if (pid) { key = 0; value = xdp_fd; } else { key = 1; value = tc_fd; } err = bpf_map_update_elem(map_fd, &key, &value, 0); While the race window is small, it has potentially serious ramifications in that triggering it would allow a BPF program to tail call to a program of a different type. So let's get rid of it by protecting the update with a spinlock. The commit in the Fixes tag is the last commit that touches the code in question. v2: - Use a spinlock instead of an atomic variable and cmpxchg() (Alexei) v3: - Put lock and the members it protects into an embedded 'owner' struct (Daniel) Fixes: 3324b584b6f6 ("ebpf: misc core cleanup") Reported-by: Lorenzo Bianconi Signed-off-by: Toke Høiland-Jørgensen Signed-off-by: Alexei Starovoitov Link: https://lore.kernel.org/bpf/20211026110019.363464-1-toke@redhat.com

bpf: Prevent increasing bpf_jit_limit above max

2021-10-23T00:23:53Z

Restrict bpf_jit_limit to the maximum supported by the arch's JIT. Signed-off-by: Lorenz Bauer Signed-off-by: Alexei Starovoitov Link: https://lore.kernel.org/bpf/20211014142554.53120-4-lmb@cloudflare.com

bpf: Exempt CAP_BPF from checks against bpf_jit_limit

2021-09-28T07:28:37Z

When introducing CAP_BPF, bpf_jit_charge_modmem() was not changed to treat programs with CAP_BPF as privileged for the purpose of JIT memory allocation. This means that a program without CAP_BPF can block a program with CAP_BPF from loading a program. Fix this by checking bpf_capable() in bpf_jit_charge_modmem(). Fixes: 2c78ee898d8f ("bpf: Implement CAP_BPF") Signed-off-by: Lorenz Bauer Signed-off-by: Daniel Borkmann Link: https://lore.kernel.org/bpf/20210922111153.19843-1-lmb@cloudflare.com

bpf: Undo off-by-one in interpreter tail call count limit

2021-08-19T16:33:37Z

The BPF interpreter as well as x86-64 BPF JIT were both in line by allowing up to 33 tail calls (however odd that number may be!). Recently, this was changed for the interpreter to reduce it down to 32 with the assumption that this should have been the actual limit "which is in line with the behavior of the x86 JITs" according to b61a28cf11d61 ("bpf: Fix off-by-one in tail call count limiting"). Paul recently reported: I'm a bit surprised by this because I had previously tested the tail call limit of several JIT compilers and found it to be 33 (i.e., allowing chains of up to 34 programs). I've just extended a test program I had to validate this again on the x86-64 JIT, and found a limit of 33 tail calls again [1]. Also note we had previously changed the RISC-V and MIPS JITs to allow up to 33 tail calls [2, 3], for consistency with other JITs and with the interpreter. We had decided to increase these two to 33 rather than decrease the other JITs to 32 for backward compatibility, though that probably doesn't matter much as I'd expect few people to actually use 33 tail calls. [1] https://github.com/pchaigno/tail-call-bench/commit/ae7887482985b4b1745c9b2ef7ff9ae506c82886 [2] 96bc4432f5ad ("bpf, riscv: Limit to 33 tail calls") [3] e49e6f6db04e ("bpf, mips: Limit to 33 tail calls") Therefore, revert b61a28cf11d61 to re-align interpreter to limit a maximum of 33 tail calls. While it is unlikely to hit the limit for the vast majority, programs in the wild could one way or another depend on this, so lets rather be a bit more conservative, and lets align the small remainder of JITs to 33. If needed in future, this limit could be slightly increased, but not decreased. Fixes: b61a28cf11d61 ("bpf: Fix off-by-one in tail call count limiting") Reported-by: Paul Chaignon Signed-off-by: Daniel Borkmann Acked-by: Andrii Nakryiko Acked-by: Johan Almbladh Acked-by: Yonghong Song Link: https://lore.kernel.org/bpf/CAO5pjwTWrC0_dzTbTHFPSqDwA56aVH+4KFGVqdq8=ASs0MqZGQ@mail.gmail.com

bpf: Allow to specify user-provided bpf_cookie for BPF perf links

2021-08-16T22:45:07Z

Add ability for users to specify custom u64 value (bpf_cookie) when creating BPF link for perf_event-backed BPF programs (kprobe/uprobe, perf_event, tracepoints). This is useful for cases when the same BPF program is used for attaching and processing invocation of different tracepoints/kprobes/uprobes in a generic fashion, but such that each invocation is distinguished from each other (e.g., BPF program can look up additional information associated with a specific kernel function without having to rely on function IP lookups). This enables new use cases to be implemented simply and efficiently that previously were possible only through code generation (and thus multiple instances of almost identical BPF program) or compilation at runtime (BCC-style) on target hosts (even more expensive resource-wise). For uprobes it is not even possible in some cases to know function IP before hand (e.g., when attaching to shared library without PID filtering, in which case base load address is not known for a library). This is done by storing u64 bpf_cookie in struct bpf_prog_array_item, corresponding to each attached and run BPF program. Given cgroup BPF programs already use two 8-byte pointers for their needs and cgroup BPF programs don't have (yet?) support for bpf_cookie, reuse that space through union of cgroup_storage and new bpf_cookie field. Make it available to kprobe/tracepoint BPF programs through bpf_trace_run_ctx. This is set by BPF_PROG_RUN_ARRAY, used by kprobe/uprobe/tracepoint BPF program execution code, which luckily is now also split from BPF_PROG_RUN_ARRAY_CG. This run context will be utilized by a new BPF helper giving access to this user-provided cookie value from inside a BPF program. Generic perf_event BPF programs will access this value from perf_event itself through passed in BPF program context. Signed-off-by: Andrii Nakryiko Signed-off-by: Daniel Borkmann Acked-by: Yonghong Song Acked-by: Peter Zijlstra (Intel) Link: https://lore.kernel.org/bpf/20210815070609.987780-6-andrii@kernel.org

bpf: Refactor BPF_PROG_RUN into a function

2021-08-16T22:45:07Z

Turn BPF_PROG_RUN into a proper always inlined function. No functional and performance changes are intended, but it makes it much easier to understand what's going on with how BPF programs are actually get executed. It's more obvious what types and callbacks are expected. Also extra () around input parameters can be dropped, as well as `__` variable prefixes intended to avoid naming collisions, which makes the code simpler to read and write. This refactoring also highlighted one extra issue. BPF_PROG_RUN is both a macro and an enum value (BPF_PROG_RUN == BPF_PROG_TEST_RUN). Turning BPF_PROG_RUN into a function causes naming conflict compilation error. So rename BPF_PROG_RUN into lower-case bpf_prog_run(), similar to bpf_prog_run_xdp(), bpf_prog_run_pin_on_cpu(), etc. All existing callers of BPF_PROG_RUN, the macro, are switched to bpf_prog_run() explicitly. Signed-off-by: Andrii Nakryiko Signed-off-by: Daniel Borkmann Acked-by: Yonghong Song Link: https://lore.kernel.org/bpf/20210815070609.987780-2-andrii@kernel.org

Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net

2021-08-13T13:41:22Z

Conflicts: drivers/net/ethernet/broadcom/bnxt/bnxt_ptp.h 9e26680733d5 ("bnxt_en: Update firmware call to retrieve TX PTP timestamp") 9e518f25802c ("bnxt_en: 1PPS functions to configure TSIO pins") 099fdeda659d ("bnxt_en: Event handler for PPS events") kernel/bpf/helpers.c include/linux/bpf-cgroup.h a2baf4e8bb0f ("bpf: Fix potentially incorrect results with bpf_get_local_storage()") c7603cfa04e7 ("bpf: Add ambient BPF runtime context stored in current") drivers/net/ethernet/mellanox/mlx5/core/pci_irq.c 5957cc557dc5 ("net/mlx5: Set all field of mlx5_irq before inserting it to the xarray") 2d0b41a37679 ("net/mlx5: Refcount mlx5_irq with integer") MAINTAINERS 7b637cd52f02 ("MAINTAINERS: fix Microchip CAN BUS Analyzer Tool entry typo") 7d901a1e878a ("net: phy: add Maxlinear GPY115/21x/24x driver") Signed-off-by: Jakub Kicinski

bpf, core: Fix kernel-doc notation

2021-08-10T11:09:28Z

Fix kernel-doc warnings in kernel/bpf/core.c (found by scripts/kernel-doc and W=1 builds). That is, correct a function name in a comment and add return descriptions for 2 functions. Fixes these kernel-doc warnings: kernel/bpf/core.c:1372: warning: expecting prototype for __bpf_prog_run(). Prototype was for ___bpf_prog_run() instead kernel/bpf/core.c:1372: warning: No description found for return value of '___bpf_prog_run' kernel/bpf/core.c:1883: warning: No description found for return value of 'bpf_prog_select_runtime' Signed-off-by: Randy Dunlap Signed-off-by: Daniel Borkmann Link: https://lore.kernel.org/bpf/20210809215229.7556-1-rdunlap@infradead.org

bpf: Fix off-by-one in tail call count limiting

2021-08-02T22:05:43Z

Before, the interpreter allowed up to MAX_TAIL_CALL_CNT + 1 tail calls. Now precisely MAX_TAIL_CALL_CNT is allowed, which is in line with the behavior of the x86 JITs. Signed-off-by: Johan Almbladh Signed-off-by: Andrii Nakryiko Acked-by: Yonghong Song Link: https://lore.kernel.org/bpf/20210728164741.350370-1-johan.almbladh@anyfinetworks.com

bpf: Introduce BPF nospec instruction for mitigating Spectre v4

2021-07-28T22:20:56Z

In case of JITs, each of the JIT backends compiles the BPF nospec instruction /either/ to a machine instruction which emits a speculation barrier /or/ to /no/ machine instruction in case the underlying architecture is not affected by Speculative Store Bypass or has different mitigations in place already. This covers both x86 and (implicitly) arm64: In case of x86, we use 'lfence' instruction for mitigation. In case of arm64, we rely on the firmware mitigation as controlled via the ssbd kernel parameter. Whenever the mitigation is enabled, it works for all of the kernel code with no need to provide any additional instructions here (hence only comment in arm64 JIT). Other archs can follow as needed. The BPF nospec instruction is specifically targeting Spectre v4 since i) we don't use a serialization barrier for the Spectre v1 case, and ii) mitigation instructions for v1 and v4 might be different on some archs. The BPF nospec is required for a future commit, where the BPF verifier does annotate intermediate BPF programs with speculation barriers. Co-developed-by: Piotr Krysiuk Co-developed-by: Benedict Schlueter Signed-off-by: Daniel Borkmann Signed-off-by: Piotr Krysiuk Signed-off-by: Benedict Schlueter Acked-by: Alexei Starovoitov