6.6-stable review patch. If anyone has any objections, please let me know.
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From: Andrei Matei andreimatei1@gmail.com
[ Upstream commit 8a021e7fa10576eeb3938328f39bbf98fe7d4715 ]
This patch simplifies the verification of size arguments associated to pointer arguments to helpers and kfuncs. Many helpers take a pointer argument followed by the size of the memory access performed to be performed through that pointer. Before this patch, the handling of the size argument in check_mem_size_reg() was confusing and wasteful: if the size register's lower bound was 0, then the verification was done twice: once considering the size of the access to be the lower-bound of the respective argument, and once considering the upper bound (even if the two are the same). The upper bound checking is a super-set of the lower-bound checking(*), except: the only point of the lower-bound check is to handle the case where zero-sized-accesses are explicitly not allowed and the lower-bound is zero. This static condition is now checked explicitly, replacing a much more complex, expensive and confusing verification call to check_helper_mem_access().
Error messages change in this patch. Before, messages about illegal zero-size accesses depended on the type of the pointer and on other conditions, and sometimes the message was plain wrong: in some tests that changed you'll see that the old message was something like "R1 min value is outside of the allowed memory range", where R1 is the pointer register; the error was wrongly claiming that the pointer was bad instead of the size being bad. Other times the information that the size came for a register with a possible range of values was wrong, and the error presented the size as a fixed zero. Now the errors refer to the right register. However, the old error messages did contain useful information about the pointer register which is now lost; recovering this information was deemed not important enough.
(*) Besides standing to reason that the checks for a bigger size access are a super-set of the checks for a smaller size access, I have also mechanically verified this by reading the code for all types of pointers. I could convince myself that it's true for all but PTR_TO_BTF_ID (check_ptr_to_btf_access). There, simply looking line-by-line does not immediately prove what we want. If anyone has any qualms, let me know.
Signed-off-by: Andrei Matei andreimatei1@gmail.com Signed-off-by: Andrii Nakryiko andrii@kernel.org Acked-by: Andrii Nakryiko andrii@kernel.org Link: https://lore.kernel.org/bpf/20231221232225.568730-2-andreimatei1@gmail.com Stable-dep-of: 8ea607330a39 ("bpf: Fix overloading of MEM_UNINIT's meaning") Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/bpf/verifier.c | 10 ++++------ .../selftests/bpf/progs/verifier_helper_value_access.c | 8 ++++---- tools/testing/selftests/bpf/progs/verifier_raw_stack.c | 2 +- 3 files changed, 9 insertions(+), 11 deletions(-)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 28b09ca5525f0..f24d570d67ca5 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -7324,12 +7324,10 @@ static int check_mem_size_reg(struct bpf_verifier_env *env, return -EACCES; }
- if (reg->umin_value == 0) { - err = check_helper_mem_access(env, regno - 1, 0, - zero_size_allowed, - meta); - if (err) - return err; + if (reg->umin_value == 0 && !zero_size_allowed) { + verbose(env, "R%d invalid zero-sized read: u64=[%lld,%lld]\n", + regno, reg->umin_value, reg->umax_value); + return -EACCES; }
if (reg->umax_value >= BPF_MAX_VAR_SIZ) { diff --git a/tools/testing/selftests/bpf/progs/verifier_helper_value_access.c b/tools/testing/selftests/bpf/progs/verifier_helper_value_access.c index 692216c0ad3d4..3e8340c2408f3 100644 --- a/tools/testing/selftests/bpf/progs/verifier_helper_value_access.c +++ b/tools/testing/selftests/bpf/progs/verifier_helper_value_access.c @@ -91,7 +91,7 @@ l0_%=: exit; \
SEC("tracepoint") __description("helper access to map: empty range") -__failure __msg("invalid access to map value, value_size=48 off=0 size=0") +__failure __msg("R2 invalid zero-sized read") __naked void access_to_map_empty_range(void) { asm volatile (" \ @@ -221,7 +221,7 @@ l0_%=: exit; \
SEC("tracepoint") __description("helper access to adjusted map (via const imm): empty range") -__failure __msg("invalid access to map value, value_size=48 off=4 size=0") +__failure __msg("R2 invalid zero-sized read") __naked void via_const_imm_empty_range(void) { asm volatile (" \ @@ -386,7 +386,7 @@ l0_%=: exit; \
SEC("tracepoint") __description("helper access to adjusted map (via const reg): empty range") -__failure __msg("R1 min value is outside of the allowed memory range") +__failure __msg("R2 invalid zero-sized read") __naked void via_const_reg_empty_range(void) { asm volatile (" \ @@ -556,7 +556,7 @@ l0_%=: exit; \
SEC("tracepoint") __description("helper access to adjusted map (via variable): empty range") -__failure __msg("R1 min value is outside of the allowed memory range") +__failure __msg("R2 invalid zero-sized read") __naked void map_via_variable_empty_range(void) { asm volatile (" \ diff --git a/tools/testing/selftests/bpf/progs/verifier_raw_stack.c b/tools/testing/selftests/bpf/progs/verifier_raw_stack.c index f67390224a9cf..7cc83acac7271 100644 --- a/tools/testing/selftests/bpf/progs/verifier_raw_stack.c +++ b/tools/testing/selftests/bpf/progs/verifier_raw_stack.c @@ -64,7 +64,7 @@ __naked void load_bytes_negative_len_2(void)
SEC("tc") __description("raw_stack: skb_load_bytes, zero len") -__failure __msg("invalid zero-sized read") +__failure __msg("R4 invalid zero-sized read: u64=[0,0]") __naked void skb_load_bytes_zero_len(void) { asm volatile (" \