Skip to content

L
linux
Switch branch/tag
  1. 08 Apr, 2018 15 commits
  3. 31 Mar, 2018 21 commits
  5. 28 Mar, 2018 4 commits
    • Greg Kroah-Hartman's avatar
      Linux 4.4.125 · aec8e72e
      Greg Kroah-Hartman authored
      aec8e72e
    • Daniel Borkmann's avatar
      bpf, x64: increase number of passes · b3ca20cb
      Daniel Borkmann authored 
      commit 6007b080 upstream.

In Cilium some of the main programs we run today are hitting 9 passes
on x64's JIT compiler, and we've had cases already where we surpassed
the limit where the JIT then punts the program to the interpreter
instead, leading to insertion failures due to CONFIG_BPF_JIT_ALWAYS_ON
or insertion failures due to the prog array owner being JITed but the
program to insert not (both must have the same JITed/non-JITed property).

One concrete case the program image shrunk from 12,767 bytes down to
10,288 bytes where the image converged after 16 steps. I've measured
that this took 340us in the JIT until it converges on my i7-6600U. Thus,
increase the original limit we had from day one where the JIT covered
cBPF only back then before we run into the case (as similar with the
complexity limit) where we trip over this and hit program rejections.
Also add a cond_resched() into the compilation loop, the JIT process
runs without any locks and may sleep anyway.
Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Acked-by: default avatarAlexei Starovoitov <ast@kernel.org>
Reviewed-by: default avatarEric Dumazet <edumazet@google.com>
Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
      b3ca20cb
    • Chenbo Feng's avatar
      bpf: skip unnecessary capability check · c9ea2f8a
      Chenbo Feng authored 
      commit 0fa4fe85 upstream.

The current check statement in BPF syscall will do a capability check
for CAP_SYS_ADMIN before checking sysctl_unprivileged_bpf_disabled. This
code path will trigger unnecessary security hooks on capability checking
and cause false alarms on unprivileged process trying to get CAP_SYS_ADMIN
access. This can be resolved by simply switch the order of the statement
and CAP_SYS_ADMIN is not required anyway if unprivileged bpf syscall is
allowed.
Signed-off-by: default avatarChenbo Feng <fengc@google.com>
Acked-by: default avatarLorenzo Colitti <lorenzo@google.com>
Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
      c9ea2f8a
    • Daniel Borkmann's avatar
      kbuild: disable clang's default use of -fmerge-all-constants · cbb5420a
      Daniel Borkmann authored 
      commit 87e0d4f0 upstream.

Prasad reported that he has seen crashes in BPF subsystem with netd
on Android with arm64 in the form of (note, the taint is unrelated):

  [ 4134.721483] Unable to handle kernel paging request at virtual address 800000001
  [ 4134.820925] Mem abort info:
  [ 4134.901283]   Exception class = DABT (current EL), IL = 32 bits
  [ 4135.016736]   SET = 0, FnV = 0
  [ 4135.119820]   EA = 0, S1PTW = 0
  [ 4135.201431] Data abort info:
  [ 4135.301388]   ISV = 0, ISS = 0x00000021
  [ 4135.359599]   CM = 0, WnR = 0
  [ 4135.470873] user pgtable: 4k pages, 39-bit VAs, pgd = ffffffe39b946000
  [ 4135.499757] [0000000800000001] *pgd=0000000000000000, *pud=0000000000000000
  [ 4135.660725] Internal error: Oops: 96000021 [#1] PREEMPT SMP
  [ 4135.674610] Modules linked in:
  [ 4135.682883] CPU: 5 PID: 1260 Comm: netd Tainted: G S      W       4.14.19+ #1
  [ 4135.716188] task: ffffffe39f4aa380 task.stack: ffffff801d4e0000
  [ 4135.731599] PC is at bpf_prog_add+0x20/0x68
  [ 4135.741746] LR is at bpf_prog_inc+0x20/0x2c
  [ 4135.751788] pc : [<ffffff94ab7ad584>] lr : [<ffffff94ab7ad638>] pstate: 60400145
  [ 4135.769062] sp : ffffff801d4e3ce0
  [...]
  [ 4136.258315] Process netd (pid: 1260, stack limit = 0xffffff801d4e0000)
  [ 4136.273746] Call trace:
  [...]
  [ 4136.442494] 3ca0: ffffff94ab7ad584 0000000060400145 ffffffe3a01bf8f8 0000000000000006
  [ 4136.460936] 3cc0: 0000008000000000 ffffff94ab844204 ffffff801d4e3cf0 ffffff94ab7ad584
  [ 4136.479241] [<ffffff94ab7ad584>] bpf_prog_add+0x20/0x68
  [ 4136.491767] [<ffffff94ab7ad638>] bpf_prog_inc+0x20/0x2c
  [ 4136.504536] [<ffffff94ab7b5d08>] bpf_obj_get_user+0x204/0x22c
  [ 4136.518746] [<ffffff94ab7ade68>] SyS_bpf+0x5a8/0x1a88

Android's netd was basically pinning the uid cookie BPF map in BPF
fs (/sys/fs/bpf/traffic_cookie_uid_map) and later on retrieving it
again resulting in above panic. Issue is that the map was wrongly
identified as a prog! Above kernel was compiled with clang 4.0,
and it turns out that clang decided to merge the bpf_prog_iops and
bpf_map_iops into a single memory location, such that the two i_ops
could then not be distinguished anymore.

Reason for this miscompilation is that clang has the more aggressive
-fmerge-all-constants enabled by default. In fact, clang source code
has a comment about it in lib/AST/ExprConstant.cpp on why it is okay
to do so:

  Pointers with different bases cannot represent the same object.
  (Note that clang defaults to -fmerge-all-constants, which can
  lead to inconsistent results for comparisons involving the address
  of a constant; this generally doesn't matter in practice.)

The issue never appeared with gcc however, since gcc does not enable
-fmerge-all-constants by default and even *explicitly* states in
it's option description that using this flag results in non-conforming
behavior, quote from man gcc:

  Languages like C or C++ require each variable, including multiple
  instances of the same variable in recursive calls, to have distinct
  locations, so using this option results in non-conforming behavior.

There are also various clang bug reports open on that matter [1],
where clang developers acknowledge the non-conforming behavior,
and refer to disabling it with -fno-merge-all-constants. But even
if this gets fixed in clang today, there are already users out there
that triggered this. Thus, fix this issue by explicitly adding
-fno-merge-all-constants to the kernel's Makefile to generically
disable this optimization, since potentially other places in the
kernel could subtly break as well.

Note, there is also a flag called -fmerge-constants (not supported
by clang), which is more conservative and only applies to strings
and it's enabled in gcc's -O/-O2/-O3/-Os optimization levels. In
gcc's code, the two flags -fmerge-{all-,}constants share the same
variable internally, so when disabling it via -fno-merge-all-constants,
then we really don't merge any const data (e.g. strings), and text
size increases with gcc (14,927,214 -> 14,942,646 for vmlinux.o).

  $ gcc -fverbose-asm -O2 foo.c -S -o foo.S
    -> foo.S lists -fmerge-constants under options enabled
  $ gcc -fverbose-asm -O2 -fno-merge-all-constants foo.c -S -o foo.S
    -> foo.S doesn't list -fmerge-constants under options enabled
  $ gcc -fverbose-asm -O2 -fno-merge-all-constants -fmerge-constants foo.c -S -o foo.S
    -> foo.S lists -fmerge-constants under options enabled

Thus, as a workaround we need to set both -fno-merge-all-constants
*and* -fmerge-constants in the Makefile in order for text size to
stay as is.

  [1] https://bugs.llvm.org/show_bug.cgi?id=18538Reported-by: default avatarPrasad Sodagudi <psodagud@codeaurora.org>
Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Chenbo Feng <fengc@google.com>
Cc: Richard Smith <richard-llvm@metafoo.co.uk>
Cc: Chandler Carruth <chandlerc@gmail.com>
Cc: linux-kernel@vger.kernel.org
Tested-by: default avatarPrasad Sodagudi <psodagud@codeaurora.org>
Acked-by: default avatarAlexei Starovoitov <ast@kernel.org>
Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
      cbb5420a
GitLab Nexedi Edition | About GitLab | About Nexedi | 沪ICP备2021021310号-2 | 沪ICP备2021021310号-7