linux-toradex.git/kernel/bpf/stackmap.c, branch v6.1-rc3

perf/bpf: Always use perf callchains if exist

2022-09-13T13:03:22+00:00

If the perf_event has PERF_SAMPLE_CALLCHAIN, BPF can use it for stack trace.
The problematic cases like PEBS and IBS already handled in the PMU driver and
they filled the callchain info in the sample data.  For others, we can call
perf_callchain() before the BPF handler.

Signed-off-by: Namhyung Kim 
Signed-off-by: Peter Zijlstra (Intel) 
Link: https://lore.kernel.org/r/20220908214104.3851807-2-namhyung@kernel.org

bpf: Compute map_btf_id during build time

2022-04-26T18:35:21+00:00

For now, the field 'map_btf_id' in 'struct bpf_map_ops' for all map
types are computed during vmlinux-btf init:

  btf_parse_vmlinux() -> btf_vmlinux_map_ids_init()

It will lookup the btf_type according to the 'map_btf_name' field in
'struct bpf_map_ops'. This process can be done during build time,
thanks to Jiri's resolve_btfids.

selftest of map_ptr has passed:

  $96 map_ptr:OK
  Summary: 1/0 PASSED, 0 SKIPPED, 0 FAILED

Reported-by: kernel test robot 
Signed-off-by: Menglong Dong 
Signed-off-by: Alexei Starovoitov

bpf: Fix excessive memory allocation in stack_map_alloc()

2022-04-08T22:28:21+00:00

The 'n_buckets * (value_size + sizeof(struct stack_map_bucket))' part of the
allocated memory for 'smap' is never used after the memlock accounting was
removed, thus get rid of it.

[ Note, Daniel:

Commit b936ca643ade ("bpf: rework memlock-based memory accounting for maps")
moved `cost += n_buckets * (value_size + sizeof(struct stack_map_bucket))`
up and therefore before the bpf_map_area_alloc() allocation, sigh. In a later
step commit c85d69135a91 ("bpf: move memory size checks to bpf_map_charge_init()"),
and the overflow checks of `cost >= U32_MAX - PAGE_SIZE` moved into
bpf_map_charge_init(). And then 370868107bf6 ("bpf: Eliminate rlimit-based
memory accounting for stackmap maps") finally removed the bpf_map_charge_init().
Anyway, the original code did the allocation same way as /after/ this fix. ]

Fixes: b936ca643ade ("bpf: rework memlock-based memory accounting for maps")
Signed-off-by: Yuntao Wang 
Signed-off-by: Daniel Borkmann 
Link: https://lore.kernel.org/bpf/20220407130423.798386-1-ytcoode@gmail.com

bpf: Remove redundant assignment to smap->map.value_size

2022-04-01T20:44:44+00:00

The attr->value_size is already assigned to smap->map.value_size
in bpf_map_init_from_attr(), there is no need to do it again in
stack_map_alloc().

Signed-off-by: Yuntao Wang 
Signed-off-by: Daniel Borkmann 
Acked-by: Joanne Koong 
Link: https://lore.kernel.org/bpf/20220323073626.958652-1-ytcoode@gmail.com

bpf: Adjust BPF stack helper functions to accommodate skip > 0

2022-03-21T02:16:23+00:00

Let's say that the caller has storage for num_elem stack frames.  Then,
the BPF stack helper functions walk the stack for only num_elem frames.
This means that if skip > 0, one keeps only 'num_elem - skip' frames.

This is because it sets init_nr in the perf_callchain_entry to the end
of the buffer to save num_elem entries only.  I believe it was because
the perf callchain code unwound the stack frames until it reached the
global max size (sysctl_perf_event_max_stack).

However it now has perf_callchain_entry_ctx.max_stack to limit the
iteration locally.  This simplifies the code to handle init_nr in the
BPF callstack entries and removes the confusion with the perf_event's
__PERF_SAMPLE_CALLCHAIN_EARLY which sets init_nr to 0.

Also change the comment on bpf_get_stack() in the header file to be
more explicit what the return value means.

Fixes: c195651e565a ("bpf: add bpf_get_stack helper")
Signed-off-by: Namhyung Kim 
Signed-off-by: Alexei Starovoitov 
Acked-by: Yonghong Song 
Link: https://lore.kernel.org/bpf/30a7b5d5-6726-1cc2-eaee-8da2828a9a9c@oracle.com
Link: https://lore.kernel.org/bpf/20220314182042.71025-1-namhyung@kernel.org

Based-on-patch-by: Eugene Loh

bpf: Cache the last valid build_id

2022-02-28T17:10:28+00:00

For binaries that are statically linked, consecutive stack frames are
likely to be in the same VMA and therefore have the same build id.

On a real-world workload, we observed that 66% of CPU cycles in
__bpf_get_stackid() were spent on build_id_parse() and find_vma().

As an optimization for this case, we can cache the previous frame's
VMA, if the new frame has the same VMA as the previous one, reuse the
previous one's build id.

We are holding the MM locks as reader across the entire loop, so we
don't need to worry about VMA going away.

Tested through "stacktrace_build_id" and "stacktrace_build_id_nmi" in
test_progs.

Suggested-by: Greg Thelen 
Signed-off-by: Hao Luo 
Signed-off-by: Daniel Borkmann 
Reviewed-by: Pasha Tatashin 
Acked-by: Andrii Nakryiko 
Acked-by: Song Liu 
Acked-by: Namhyung Kim 
Link: https://lore.kernel.org/bpf/20220224000531.1265030-1-haoluo@google.com

bpf: Guard against accessing NULL pt_regs in bpf_get_task_stack()

2022-01-15T01:21:23+00:00

task_pt_regs() can return NULL on powerpc for kernel threads. This is
then used in __bpf_get_stack() to check for user mode, resulting in a
kernel oops. Guard against this by checking return value of
task_pt_regs() before trying to obtain the call chain.

Fixes: fa28dcb82a38f8 ("bpf: Introduce helper bpf_get_task_stack()")
Cc: stable@vger.kernel.org # v5.9+
Signed-off-by: Naveen N. Rao 
Acked-by: Daniel Borkmann 
Signed-off-by: Michael Ellerman 
Link: https://lore.kernel.org/r/d5ef83c361cc255494afd15ff1b4fb02a36e1dcf.1641468127.git.naveen.n.rao@linux.vnet.ibm.com

bpf: Introduce btf_tracing_ids

2021-11-12T18:19:09+00:00

Similar to btf_sock_ids, btf_tracing_ids provides btf ID for task_struct,
file, and vm_area_struct via easy to understand format like
btf_tracing_ids[BTF_TRACING_TYPE_[TASK|file|VMA]].

Suggested-by: Alexei Starovoitov 
Signed-off-by: Song Liu 
Signed-off-by: Alexei Starovoitov 
Acked-by: Yonghong Song 
Link: https://lore.kernel.org/bpf/20211112150243.1270987-3-songliubraving@fb.com

bpf: Introduce helper bpf_find_vma

2021-11-07T19:54:51+00:00

In some profiler use cases, it is necessary to map an address to the
backing file, e.g., a shared library. bpf_find_vma helper provides a
flexible way to achieve this. bpf_find_vma maps an address of a task to
the vma (vm_area_struct) for this address, and feed the vma to an callback
BPF function. The callback function is necessary here, as we need to
ensure mmap_sem is unlocked.

It is necessary to lock mmap_sem for find_vma. To lock and unlock mmap_sem
safely when irqs are disable, we use the same mechanism as stackmap with
build_id. Specifically, when irqs are disabled, the unlocked is postponed
in an irq_work. Refactor stackmap.c so that the irq_work is shared among
bpf_find_vma and stackmap helpers.

Signed-off-by: Song Liu 
Signed-off-by: Alexei Starovoitov 
Tested-by: Hengqi Chen 
Acked-by: Yonghong Song 
Link: https://lore.kernel.org/bpf/20211105232330.1936330-2-songliubraving@fb.com

bpf: Fix integer overflow in prealloc_elems_and_freelist()

2021-09-30T14:17:23+00:00

In prealloc_elems_and_freelist(), the multiplication to calculate the
size passed to bpf_map_area_alloc() could lead to an integer overflow.
As a result, out-of-bounds write could occur in pcpu_freelist_populate()
as reported by KASAN:

[...]
[   16.968613] BUG: KASAN: slab-out-of-bounds in pcpu_freelist_populate+0xd9/0x100
[   16.969408] Write of size 8 at addr ffff888104fc6ea0 by task crash/78
[   16.970038]
[   16.970195] CPU: 0 PID: 78 Comm: crash Not tainted 5.15.0-rc2+ #1
[   16.970878] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.13.0-1ubuntu1.1 04/01/2014
[   16.972026] Call Trace:
[   16.972306]  dump_stack_lvl+0x34/0x44
[   16.972687]  print_address_description.constprop.0+0x21/0x140
[   16.973297]  ? pcpu_freelist_populate+0xd9/0x100
[   16.973777]  ? pcpu_freelist_populate+0xd9/0x100
[   16.974257]  kasan_report.cold+0x7f/0x11b
[   16.974681]  ? pcpu_freelist_populate+0xd9/0x100
[   16.975190]  pcpu_freelist_populate+0xd9/0x100
[   16.975669]  stack_map_alloc+0x209/0x2a0
[   16.976106]  __sys_bpf+0xd83/0x2ce0
[...]

The possibility of this overflow was originally discussed in [0], but
was overlooked.

Fix the integer overflow by changing elem_size to u64 from u32.

  [0] https://lore.kernel.org/bpf/728b238e-a481-eb50-98e9-b0f430ab01e7@gmail.com/

Fixes: 557c0c6e7df8 ("bpf: convert stackmap to pre-allocation")
Signed-off-by: Tatsuhiko Yasumatsu 
Signed-off-by: Daniel Borkmann 
Link: https://lore.kernel.org/bpf/20210930135545.173698-1-th.yasumatsu@gmail.com