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From: Daniel Borkmann <daniel@iogearbox.net>
To: bpf@vger.kernel.org
Cc: netdev@vger.kernel.org, ast@kernel.org,
	andrii.nakryiko@gmail.com, john.fastabend@gmail.com,
	Daniel Borkmann <daniel@iogearbox.net>,
	Andrii Nakryiko <andriin@fb.com>,
	Masami Hiramatsu <mhiramat@kernel.org>
Subject: [PATCH bpf-next v3 1/8] uaccess: Add non-pagefault user-space write function
Date: Sat,  2 Nov 2019 00:17:56 +0100
Message-ID: <9df2542e68141bfa3addde631441ee45503856a8.1572649915.git.daniel@iogearbox.net> (raw)
In-Reply-To: <cover.1572649915.git.daniel@iogearbox.net>

Commit 3d7081822f7f ("uaccess: Add non-pagefault user-space read functions")
missed to add probe write function, therefore factor out a probe_write_common()
helper with most logic of probe_kernel_write() except setting KERNEL_DS, and
add a new probe_user_write() helper so it can be used from BPF side.

Again, on some archs, the user address space and kernel address space can
co-exist and be overlapping, so in such case, setting KERNEL_DS would mean
that the given address is treated as being in kernel address space.

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
---
 include/linux/uaccess.h | 12 +++++++++++
 mm/maccess.c            | 45 +++++++++++++++++++++++++++++++++++++----
 2 files changed, 53 insertions(+), 4 deletions(-)

diff --git a/include/linux/uaccess.h b/include/linux/uaccess.h
index d4ee6e942562..38555435a64a 100644
--- a/include/linux/uaccess.h
+++ b/include/linux/uaccess.h
@@ -337,6 +337,18 @@ extern long __probe_user_read(void *dst, const void __user *src, size_t size);
 extern long notrace probe_kernel_write(void *dst, const void *src, size_t size);
 extern long notrace __probe_kernel_write(void *dst, const void *src, size_t size);
 
+/*
+ * probe_user_write(): safely attempt to write to a location in user space
+ * @dst: address to write to
+ * @src: pointer to the data that shall be written
+ * @size: size of the data chunk
+ *
+ * Safely write to address @dst from the buffer at @src.  If a kernel fault
+ * happens, handle that and return -EFAULT.
+ */
+extern long notrace probe_user_write(void __user *dst, const void *src, size_t size);
+extern long notrace __probe_user_write(void __user *dst, const void *src, size_t size);
+
 extern long strncpy_from_unsafe(char *dst, const void *unsafe_addr, long count);
 extern long strncpy_from_unsafe_user(char *dst, const void __user *unsafe_addr,
 				     long count);
diff --git a/mm/maccess.c b/mm/maccess.c
index d065736f6b87..2d3c3d01064c 100644
--- a/mm/maccess.c
+++ b/mm/maccess.c
@@ -18,6 +18,18 @@ probe_read_common(void *dst, const void __user *src, size_t size)
 	return ret ? -EFAULT : 0;
 }
 
+static __always_inline long
+probe_write_common(void __user *dst, const void *src, size_t size)
+{
+	long ret;
+
+	pagefault_disable();
+	ret = __copy_to_user_inatomic(dst, src, size);
+	pagefault_enable();
+
+	return ret ? -EFAULT : 0;
+}
+
 /**
  * probe_kernel_read(): safely attempt to read from a kernel-space location
  * @dst: pointer to the buffer that shall take the data
@@ -85,6 +97,7 @@ EXPORT_SYMBOL_GPL(probe_user_read);
  * Safely write to address @dst from the buffer at @src.  If a kernel fault
  * happens, handle that and return -EFAULT.
  */
+
 long __weak probe_kernel_write(void *dst, const void *src, size_t size)
     __attribute__((alias("__probe_kernel_write")));
 
@@ -94,15 +107,39 @@ long __probe_kernel_write(void *dst, const void *src, size_t size)
 	mm_segment_t old_fs = get_fs();
 
 	set_fs(KERNEL_DS);
-	pagefault_disable();
-	ret = __copy_to_user_inatomic((__force void __user *)dst, src, size);
-	pagefault_enable();
+	ret = probe_write_common((__force void __user *)dst, src, size);
 	set_fs(old_fs);
 
-	return ret ? -EFAULT : 0;
+	return ret;
 }
 EXPORT_SYMBOL_GPL(probe_kernel_write);
 
+/**
+ * probe_user_write(): safely attempt to write to a user-space location
+ * @dst: address to write to
+ * @src: pointer to the data that shall be written
+ * @size: size of the data chunk
+ *
+ * Safely write to address @dst from the buffer at @src.  If a kernel fault
+ * happens, handle that and return -EFAULT.
+ */
+
+long __weak probe_user_write(void __user *dst, const void *src, size_t size)
+    __attribute__((alias("__probe_user_write")));
+
+long __probe_user_write(void __user *dst, const void *src, size_t size)
+{
+	long ret = -EFAULT;
+	mm_segment_t old_fs = get_fs();
+
+	set_fs(USER_DS);
+	if (access_ok(dst, size))
+		ret = probe_write_common(dst, src, size);
+	set_fs(old_fs);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(probe_user_write);
 
 /**
  * strncpy_from_unsafe: - Copy a NUL terminated string from unsafe address.
-- 
2.21.0


  reply index

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-11-01 23:17 [PATCH bpf-next v3 0/8] Fix BPF probe memory helpers Daniel Borkmann
2019-11-01 23:17 ` Daniel Borkmann [this message]
2019-11-01 23:17 ` [PATCH bpf-next v3 2/8] uaccess: Add strict non-pagefault kernel-space read function Daniel Borkmann
2019-11-01 23:17 ` [PATCH bpf-next v3 3/8] bpf: Make use of probe_user_write in probe write helper Daniel Borkmann
2019-11-01 23:17 ` [PATCH bpf-next v3 4/8] bpf: Add probe_read_{user,kernel} and probe_read_{user,kernel}_str helpers Daniel Borkmann
2019-11-01 23:18 ` [PATCH bpf-next v3 5/8] bpf: Switch BPF probe insns to bpf_probe_read_kernel Daniel Borkmann
2019-11-01 23:18 ` [PATCH bpf-next v3 6/8] bpf, samples: Use bpf_probe_read_user where appropriate Daniel Borkmann
2019-11-01 23:18 ` [PATCH bpf-next v3 7/8] bpf, testing: Convert prog tests to probe_read_{user,kernel}{,_str} helper Daniel Borkmann
2019-11-01 23:18 ` [PATCH bpf-next v3 8/8] bpf, testing: Add selftest to read/write sockaddr from user space Daniel Borkmann
2019-11-02 20:08 ` [PATCH bpf-next v3 0/8] Fix BPF probe memory helpers Alexei Starovoitov

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