ACK: [Eoan][SRU][PATCH 1/1] bpf: fix accessing bpf_sysctl.file_pos on s390
Colin Ian King
colin.king at canonical.com
Fri Feb 7 10:59:13 UTC 2020
On 07/02/2020 06:47, Po-Hsu Lin wrote:
> From: Ilya Leoshkevich <iii at linux.ibm.com>
>
> BugLink: https://bugs.launchpad.net/bugs/1862263
>
> "ctx:file_pos sysctl:read write ok" fails on s390 with "Read value !=
> nux". This is because verifier rewrites a complete 32-bit
> bpf_sysctl.file_pos update to a partial update of the first 32 bits of
> 64-bit *bpf_sysctl_kern.ppos, which is not correct on big-endian
> systems.
>
> Fix by using an offset on big-endian systems.
>
> Ditto for bpf_sysctl.file_pos reads. Currently the test does not detect
> a problem there, since it expects to see 0, which it gets with high
> probability in error cases, so change it to seek to offset 3 and expect
> 3 in bpf_sysctl.file_pos.
>
> Fixes: e1550bfe0de4 ("bpf: Add file_pos field to bpf_sysctl ctx")
> Signed-off-by: Ilya Leoshkevich <iii at linux.ibm.com>
> Acked-by: Yonghong Song <yhs at fb.com>
> Signed-off-by: Daniel Borkmann <daniel at iogearbox.net>
> Link: https://lore.kernel.org/bpf/20190816105300.49035-1-iii@linux.ibm.com/
> (cherry picked from commit d895a0f16fadb26d22ab531c49768f7642ae5c3e)
> Signed-off-by: Po-Hsu Lin <po-hsu.lin at canonical.com>
> ---
> include/linux/filter.h | 8 ++++----
> kernel/bpf/cgroup.c | 10 ++++++++--
> kernel/bpf/verifier.c | 4 ++--
> tools/testing/selftests/bpf/test_sysctl.c | 9 ++++++++-
> 4 files changed, 22 insertions(+), 9 deletions(-)
>
> diff --git a/include/linux/filter.h b/include/linux/filter.h
> index 38716f9..0367a75 100644
> --- a/include/linux/filter.h
> +++ b/include/linux/filter.h
> @@ -749,14 +749,14 @@ bpf_ctx_narrow_access_ok(u32 off, u32 size, u32 size_default)
> }
>
> static inline u8
> -bpf_ctx_narrow_load_shift(u32 off, u32 size, u32 size_default)
> +bpf_ctx_narrow_access_offset(u32 off, u32 size, u32 size_default)
> {
> - u8 load_off = off & (size_default - 1);
> + u8 access_off = off & (size_default - 1);
>
> #ifdef __LITTLE_ENDIAN
> - return load_off * 8;
> + return access_off;
> #else
> - return (size_default - (load_off + size)) * 8;
> + return size_default - (access_off + size);
> #endif
> }
>
> diff --git a/kernel/bpf/cgroup.c b/kernel/bpf/cgroup.c
> index 9ad7cd3..521e341 100644
> --- a/kernel/bpf/cgroup.c
> +++ b/kernel/bpf/cgroup.c
> @@ -1325,6 +1325,7 @@ static u32 sysctl_convert_ctx_access(enum bpf_access_type type,
> struct bpf_prog *prog, u32 *target_size)
> {
> struct bpf_insn *insn = insn_buf;
> + u32 read_size;
>
> switch (si->off) {
> case offsetof(struct bpf_sysctl, write):
> @@ -1356,7 +1357,9 @@ static u32 sysctl_convert_ctx_access(enum bpf_access_type type,
> treg, si->dst_reg,
> offsetof(struct bpf_sysctl_kern, ppos));
> *insn++ = BPF_STX_MEM(
> - BPF_SIZEOF(u32), treg, si->src_reg, 0);
> + BPF_SIZEOF(u32), treg, si->src_reg,
> + bpf_ctx_narrow_access_offset(
> + 0, sizeof(u32), sizeof(loff_t)));
> *insn++ = BPF_LDX_MEM(
> BPF_DW, treg, si->dst_reg,
> offsetof(struct bpf_sysctl_kern, tmp_reg));
> @@ -1365,8 +1368,11 @@ static u32 sysctl_convert_ctx_access(enum bpf_access_type type,
> BPF_FIELD_SIZEOF(struct bpf_sysctl_kern, ppos),
> si->dst_reg, si->src_reg,
> offsetof(struct bpf_sysctl_kern, ppos));
> + read_size = bpf_size_to_bytes(BPF_SIZE(si->code));
> *insn++ = BPF_LDX_MEM(
> - BPF_SIZE(si->code), si->dst_reg, si->dst_reg, 0);
> + BPF_SIZE(si->code), si->dst_reg, si->dst_reg,
> + bpf_ctx_narrow_access_offset(
> + 0, read_size, sizeof(loff_t)));
> }
> *target_size = sizeof(u32);
> break;
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index 72161f5d..3c9f9c4 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -8641,8 +8641,8 @@ static int convert_ctx_accesses(struct bpf_verifier_env *env)
> }
>
> if (is_narrower_load && size < target_size) {
> - u8 shift = bpf_ctx_narrow_load_shift(off, size,
> - size_default);
> + u8 shift = bpf_ctx_narrow_access_offset(
> + off, size, size_default) * 8;
> if (ctx_field_size <= 4) {
> if (shift)
> insn_buf[cnt++] = BPF_ALU32_IMM(BPF_RSH,
> diff --git a/tools/testing/selftests/bpf/test_sysctl.c b/tools/testing/selftests/bpf/test_sysctl.c
> index c938f17..70e2e96 100644
> --- a/tools/testing/selftests/bpf/test_sysctl.c
> +++ b/tools/testing/selftests/bpf/test_sysctl.c
> @@ -31,6 +31,7 @@ struct sysctl_test {
> enum bpf_attach_type attach_type;
> const char *sysctl;
> int open_flags;
> + int seek;
> const char *newval;
> const char *oldval;
> enum {
> @@ -139,7 +140,7 @@ static struct sysctl_test tests[] = {
> /* If (file_pos == X) */
> BPF_LDX_MEM(BPF_W, BPF_REG_7, BPF_REG_1,
> offsetof(struct bpf_sysctl, file_pos)),
> - BPF_JMP_IMM(BPF_JNE, BPF_REG_7, 0, 2),
> + BPF_JMP_IMM(BPF_JNE, BPF_REG_7, 3, 2),
>
> /* return ALLOW; */
> BPF_MOV64_IMM(BPF_REG_0, 1),
> @@ -152,6 +153,7 @@ static struct sysctl_test tests[] = {
> .attach_type = BPF_CGROUP_SYSCTL,
> .sysctl = "kernel/ostype",
> .open_flags = O_RDONLY,
> + .seek = 3,
> .result = SUCCESS,
> },
> {
> @@ -1448,6 +1450,11 @@ static int access_sysctl(const char *sysctl_path,
> if (fd < 0)
> return fd;
>
> + if (test->seek && lseek(fd, test->seek, SEEK_SET) == -1) {
> + log_err("lseek(%d) failed", test->seek);
> + goto err;
> + }
> +
> if (test->open_flags == O_RDONLY) {
> char buf[128];
>
>
Upstream cherry pick with positive test results. LGTM,
Acked-by: Colin Ian King <colin.king at canonical.com>
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