From: Jiong Wang jiong.wang@netronome.com
commit 0bae2d4d62d523f06ff1a8e88ce38b45400acd28 upstream.
Verifier is supposed to support sharing stack slot allocated to ptr with SCALAR_VALUE for privileged program. However this doesn't happen for some cases.
The reason is verifier is not clearing slot_type STACK_SPILL for all bytes, it only clears part of them, while verifier is using:
slot_type[0] == STACK_SPILL
as a convention to check one slot is ptr type.
So, the consequence of partial clearing slot_type is verifier could treat a partially overridden ptr slot, which should now be a SCALAR_VALUE slot, still as ptr slot, and rejects some valid programs.
Before this patch, test_xdp_noinline.o under bpf selftests, bpf_lxc.o and bpf_netdev.o under Cilium bpf repo, when built with -mattr=+alu32 are rejected due to this issue. After this patch, they all accepted.
There is no processed insn number change before and after this patch on Cilium bpf programs.
Reviewed-by: Jakub Kicinski jakub.kicinski@netronome.com Signed-off-by: Jiong Wang jiong.wang@netronome.com Reviewed-by: Daniel Borkmann daniel@iogearbox.net Signed-off-by: Alexei Starovoitov ast@kernel.org [OP: adjusted context for 4.19] Signed-off-by: Ovidiu Panait ovidiu.panait@windriver.com --- kernel/bpf/verifier.c | 5 +++ tools/testing/selftests/bpf/test_verifier.c | 34 +++++++++++++++++++-- 2 files changed, 37 insertions(+), 2 deletions(-)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index a5259ff30073..b6f008dcb30c 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -1039,6 +1039,10 @@ static int check_stack_write(struct bpf_verifier_env *env,
/* regular write of data into stack destroys any spilled ptr */ state->stack[spi].spilled_ptr.type = NOT_INIT; + /* Mark slots as STACK_MISC if they belonged to spilled ptr. */ + if (state->stack[spi].slot_type[0] == STACK_SPILL) + for (i = 0; i < BPF_REG_SIZE; i++) + state->stack[spi].slot_type[i] = STACK_MISC;
/* only mark the slot as written if all 8 bytes were written * otherwise read propagation may incorrectly stop too soon @@ -1056,6 +1060,7 @@ static int check_stack_write(struct bpf_verifier_env *env, register_is_null(&cur->regs[value_regno])) type = STACK_ZERO;
+ /* Mark slots affected by this stack write. */ for (i = 0; i < size; i++) state->stack[spi].slot_type[(slot - i) % BPF_REG_SIZE] = type; diff --git a/tools/testing/selftests/bpf/test_verifier.c b/tools/testing/selftests/bpf/test_verifier.c index c7d17781dbfe..6b9ed915c6b0 100644 --- a/tools/testing/selftests/bpf/test_verifier.c +++ b/tools/testing/selftests/bpf/test_verifier.c @@ -956,15 +956,45 @@ static struct bpf_test tests[] = { BPF_STX_MEM(BPF_DW, BPF_REG_10, BPF_REG_1, -8), /* mess up with R1 pointer on stack */ BPF_ST_MEM(BPF_B, BPF_REG_10, -7, 0x23), - /* fill back into R0 should fail */ + /* fill back into R0 is fine for priv. + * R0 now becomes SCALAR_VALUE. + */ BPF_LDX_MEM(BPF_DW, BPF_REG_0, BPF_REG_10, -8), + /* Load from R0 should fail. */ + BPF_LDX_MEM(BPF_DW, BPF_REG_0, BPF_REG_0, 8), BPF_EXIT_INSN(), }, .errstr_unpriv = "attempt to corrupt spilled", - .errstr = "corrupted spill", + .errstr = "R0 invalid mem access 'inv", .result = REJECT, .flags = F_NEEDS_EFFICIENT_UNALIGNED_ACCESS, }, + { + "check corrupted spill/fill, LSB", + .insns = { + BPF_STX_MEM(BPF_DW, BPF_REG_10, BPF_REG_1, -8), + BPF_ST_MEM(BPF_H, BPF_REG_10, -8, 0xcafe), + BPF_LDX_MEM(BPF_DW, BPF_REG_0, BPF_REG_10, -8), + BPF_EXIT_INSN(), + }, + .errstr_unpriv = "attempt to corrupt spilled", + .result_unpriv = REJECT, + .result = ACCEPT, + .retval = POINTER_VALUE, + }, + { + "check corrupted spill/fill, MSB", + .insns = { + BPF_STX_MEM(BPF_DW, BPF_REG_10, BPF_REG_1, -8), + BPF_ST_MEM(BPF_W, BPF_REG_10, -4, 0x12345678), + BPF_LDX_MEM(BPF_DW, BPF_REG_0, BPF_REG_10, -8), + BPF_EXIT_INSN(), + }, + .errstr_unpriv = "attempt to corrupt spilled", + .result_unpriv = REJECT, + .result = ACCEPT, + .retval = POINTER_VALUE, + }, { "invalid src register in STX", .insns = {