From: Ilya Leoshkevich <iii@linux.ibm.com>
To: Daniel Borkmann <daniel@iogearbox.net>,
Alexei Starovoitov <ast@kernel.org>
Cc: bpf@vger.kernel.org, Heiko Carstens <heiko.carstens@de.ibm.com>,
Vasily Gorbik <gor@linux.ibm.com>,
Ilya Leoshkevich <iii@linux.ibm.com>
Subject: [PATCH bpf] bpf: fix accessing bpf_sysctl.file_pos on s390
Date: Thu, 15 Aug 2019 13:20:44 +0200 [thread overview]
Message-ID: <20190815112044.38420-1-iii@linux.ibm.com> (raw)
"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@linux.ibm.com>
---
include/linux/filter.h | 10 ++++++++++
kernel/bpf/cgroup.c | 9 +++++++--
tools/testing/selftests/bpf/test_sysctl.c | 9 ++++++++-
3 files changed, 25 insertions(+), 3 deletions(-)
diff --git a/include/linux/filter.h b/include/linux/filter.h
index 92c6e31fb008..94e81c56d81c 100644
--- a/include/linux/filter.h
+++ b/include/linux/filter.h
@@ -760,6 +760,16 @@ bpf_ctx_narrow_load_shift(u32 off, u32 size, u32 size_default)
#endif
}
+static inline s16
+bpf_ctx_narrow_access_offset(size_t variable_size, size_t access_size)
+{
+#ifdef __LITTLE_ENDIAN
+ return 0;
+#else
+ return variable_size - access_size;
+#endif
+}
+
#define bpf_ctx_wide_access_ok(off, size, type, field) \
(size == sizeof(__u64) && \
off >= offsetof(type, field) && \
diff --git a/kernel/bpf/cgroup.c b/kernel/bpf/cgroup.c
index 0a00eaca6fae..b835fbb13ea8 100644
--- a/kernel/bpf/cgroup.c
+++ b/kernel/bpf/cgroup.c
@@ -1356,7 +1356,9 @@ 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(
+ sizeof(loff_t), sizeof(u32)));
*insn++ = BPF_LDX_MEM(
BPF_DW, treg, si->dst_reg,
offsetof(struct bpf_sysctl_kern, tmp_reg));
@@ -1366,7 +1368,10 @@ static u32 sysctl_convert_ctx_access(enum bpf_access_type type,
si->dst_reg, si->src_reg,
offsetof(struct bpf_sysctl_kern, ppos));
*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(
+ sizeof(loff_t),
+ bpf_size_to_bytes(BPF_SIZE(si->code))));
}
*target_size = sizeof(u32);
break;
diff --git a/tools/testing/selftests/bpf/test_sysctl.c b/tools/testing/selftests/bpf/test_sysctl.c
index a3bebd7c68dd..abc26248a7f1 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,
},
{
@@ -1442,6 +1444,11 @@ 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];
--
2.21.0
next reply other threads:[~2019-08-15 11:20 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-15 11:20 Ilya Leoshkevich [this message]
2019-08-15 19:58 ` [PATCH bpf] bpf: fix accessing bpf_sysctl.file_pos on s390 Andrey Ignatov
2019-08-15 23:01 ` Yonghong Song
2019-08-16 10:34 ` Ilya Leoshkevich
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20190815112044.38420-1-iii@linux.ibm.com \
--to=iii@linux.ibm.com \
--cc=ast@kernel.org \
--cc=bpf@vger.kernel.org \
--cc=daniel@iogearbox.net \
--cc=gor@linux.ibm.com \
--cc=heiko.carstens@de.ibm.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).