From: Andrii Nakryiko <andrii@kernel.org> stable inclusion from stable-5.10.80 commit 19337ed10e7e7d36b017b40d08eece6ab428d3af bugzilla: 185821 https://gitee.com/openeuler/kernel/issues/I4L7CG Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=... -------------------------------- [ Upstream commit 0133c20480b14820d43c37c0e9502da4bffcad3a ] After most recent nightly Clang update strobemeta selftests started failing with the following error (relevant portion of assembly included): 1624: (85) call bpf_probe_read_user_str#114 1625: (bf) r1 = r0 1626: (18) r2 = 0xfffffffe 1628: (5f) r1 &= r2 1629: (55) if r1 != 0x0 goto pc+7 1630: (07) r9 += 104 1631: (6b) *(u16 *)(r9 +0) = r0 1632: (67) r0 <<= 32 1633: (77) r0 >>= 32 1634: (79) r1 = *(u64 *)(r10 -456) 1635: (0f) r1 += r0 1636: (7b) *(u64 *)(r10 -456) = r1 1637: (79) r1 = *(u64 *)(r10 -368) 1638: (c5) if r1 s< 0x1 goto pc+778 1639: (bf) r6 = r8 1640: (0f) r6 += r7 1641: (b4) w1 = 0 1642: (6b) *(u16 *)(r6 +108) = r1 1643: (79) r3 = *(u64 *)(r10 -352) 1644: (79) r9 = *(u64 *)(r10 -456) 1645: (bf) r1 = r9 1646: (b4) w2 = 1 1647: (85) call bpf_probe_read_user_str#114 R1 unbounded memory access, make sure to bounds check any such access In the above code r0 and r1 are implicitly related. Clang knows that, but verifier isn't able to infer this relationship. Yonghong Song narrowed down this "regression" in code generation to a recent Clang optimization change ([0]), which for BPF target generates code pattern that BPF verifier can't handle and loses track of register boundaries. This patch works around the issue by adding an BPF assembly-based helper that helps to prove to the verifier that upper bound of the register is a given constant by controlling the exact share of generated BPF instruction sequence. This fixes the immediate issue for strobemeta selftest. [0] https://github.com/llvm/llvm-project/commit/acabad9ff6bf13e00305d9d8621ee8ea... Signed-off-by: Andrii Nakryiko <andrii@kernel.org> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Yonghong Song <yhs@fb.com> Link: https://lore.kernel.org/bpf/20211029182907.166910-1-andrii@kernel.org Signed-off-by: Sasha Levin <sashal@kernel.org> Signed-off-by: Chen Jun <chenjun102@huawei.com> Reviewed-by: Weilong Chen <chenweilong@huawei.com> Acked-by: Weilong Chen <chenweilong@huawei.com> Signed-off-by: Chen Jun <chenjun102@huawei.com> Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com> --- tools/testing/selftests/bpf/progs/strobemeta.h | 11 +++++++++++ 1 file changed, 11 insertions(+) diff --git a/tools/testing/selftests/bpf/progs/strobemeta.h b/tools/testing/selftests/bpf/progs/strobemeta.h index 7de534f38c3f..3687ea755ab5 100644 --- a/tools/testing/selftests/bpf/progs/strobemeta.h +++ b/tools/testing/selftests/bpf/progs/strobemeta.h @@ -10,6 +10,14 @@ #include <linux/types.h> #include <bpf/bpf_helpers.h> +#define bpf_clamp_umax(VAR, UMAX) \ + asm volatile ( \ + "if %0 <= %[max] goto +1\n" \ + "%0 = %[max]\n" \ + : "+r"(VAR) \ + : [max]"i"(UMAX) \ + ) + typedef uint32_t pid_t; struct task_struct {}; @@ -413,6 +421,7 @@ static __always_inline void *read_map_var(struct strobemeta_cfg *cfg, len = bpf_probe_read_user_str(payload, STROBE_MAX_STR_LEN, map.tag); if (len <= STROBE_MAX_STR_LEN) { + bpf_clamp_umax(len, STROBE_MAX_STR_LEN); descr->tag_len = len; payload += len; } @@ -430,6 +439,7 @@ static __always_inline void *read_map_var(struct strobemeta_cfg *cfg, len = bpf_probe_read_user_str(payload, STROBE_MAX_STR_LEN, map.entries[i].key); if (len <= STROBE_MAX_STR_LEN) { + bpf_clamp_umax(len, STROBE_MAX_STR_LEN); descr->key_lens[i] = len; payload += len; } @@ -437,6 +447,7 @@ static __always_inline void *read_map_var(struct strobemeta_cfg *cfg, len = bpf_probe_read_user_str(payload, STROBE_MAX_STR_LEN, map.entries[i].val); if (len <= STROBE_MAX_STR_LEN) { + bpf_clamp_umax(len, STROBE_MAX_STR_LEN); descr->val_lens[i] = len; payload += len; } -- 2.20.1