LKML Archive on lore.kernel.org
 help / color / Atom feed
From: Masami Hiramatsu <mhiramat@kernel.org>
To: Steven Rostedt <rostedt@goodmis.org>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Shuah Khan <shuah@kernel.org>,
	Arnaldo Carvalho de Melo <acme@kernel.org>,
	Peter Zijlstra <peterz@infradead.org>
Cc: mhiramat@kernel.org, linux-kernel@vger.kernel.org,
	Andy Lutomirski <luto@amacapital.net>,
	Ingo Molnar <mingo@kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Changbin Du <changbin.du@gmail.com>, Jann Horn <jannh@google.com>,
	Kees Cook <keescook@chromium.org>,
	Andy Lutomirski <luto@kernel.org>,
	Alexei Starovoitov <alexei.starovoitov@gmail.com>,
	Nadav Amit <namit@vmware.com>,
	Joel Fernandes <joel@joelfernandes.org>,
	yhs@fb.com
Subject: [PATCH -tip v9 2/6] uaccess: Add non-pagefault user-space read functions
Date: Wed, 15 May 2019 14:38:18 +0900
Message-ID: <155789869802.26965.4940338412595759063.stgit@devnote2> (raw)
In-Reply-To: <155789866428.26965.8344923934342528416.stgit@devnote2>

Add probe_user_read(), strncpy_from_unsafe_user() and
strnlen_unsafe_user() which allows caller to access user-space
in IRQ context.

Current probe_kernel_read() and strncpy_from_unsafe() are
not available for user-space memory, because it sets
KERNEL_DS while accessing data. On some arch, user address
space and kernel address space can be co-exist, but others
can not. In that case, setting KERNEL_DS means given
address is treated as a kernel address space.
Also strnlen_user() is only available from user context since
it can sleep if pagefault is enabled.

To access user-space memory without pagefault, we need
these new functions which sets USER_DS while accessing
the data.

Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Acked-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
  Changes in v8:
   - Fix style issues and typos according to Ingo's comment (Thanks!)
  Changes in v6:
   - Remove user_access_ok()
  Changes in v5:
   - Simplify probe_user_read() (Thanks, Peter!)
   - Add strnlen_unsafe_user()
  Changes in v3:
   - Use user_access_ok() for probe_user_read().
  Changes in v2:
   - Simplify strncpy_from_unsafe_user() using strncpy_from_user()
     according to Linus's suggestion.
   - Simplify probe_user_read() not using intermediate function.
---
 include/linux/uaccess.h |   14 +++++
 mm/maccess.c            |  122 +++++++++++++++++++++++++++++++++++++++++++++--
 2 files changed, 130 insertions(+), 6 deletions(-)

diff --git a/include/linux/uaccess.h b/include/linux/uaccess.h
index 5a43ef7db492..9c435c3f2105 100644
--- a/include/linux/uaccess.h
+++ b/include/linux/uaccess.h
@@ -242,6 +242,17 @@ static inline unsigned long __copy_from_user_inatomic_nocache(void *to,
 extern long probe_kernel_read(void *dst, const void *src, size_t size);
 extern long __probe_kernel_read(void *dst, const void *src, size_t size);
 
+/*
+ * probe_user_read(): safely attempt to read from a location in user space
+ * @dst: pointer to the buffer that shall take the data
+ * @src: address to read from
+ * @size: size of the data chunk
+ *
+ * Safely read from address @src to the buffer at @dst.  If a kernel fault
+ * happens, handle that and return -EFAULT.
+ */
+extern long probe_user_read(void *dst, const void __user *src, size_t size);
+
 /*
  * probe_kernel_write(): safely attempt to write to a location
  * @dst: address to write to
@@ -255,6 +266,9 @@ 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);
 
 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);
+extern long strnlen_unsafe_user(const void __user *unsafe_addr, long count);
 
 /**
  * probe_kernel_address(): safely attempt to read from a location
diff --git a/mm/maccess.c b/mm/maccess.c
index ec00be51a24f..19c8c3dc14df 100644
--- a/mm/maccess.c
+++ b/mm/maccess.c
@@ -5,8 +5,20 @@
 #include <linux/mm.h>
 #include <linux/uaccess.h>
 
+static __always_inline long
+probe_read_common(void *dst, const void __user *src, size_t size)
+{
+	long ret;
+
+	pagefault_disable();
+	ret = __copy_from_user_inatomic(dst, src, size);
+	pagefault_enable();
+
+	return ret ? -EFAULT : 0;
+}
+
 /**
- * probe_kernel_read(): safely attempt to read from a location
+ * probe_kernel_read(): safely attempt to read from a kernel-space location
  * @dst: pointer to the buffer that shall take the data
  * @src: address to read from
  * @size: size of the data chunk
@@ -29,16 +41,40 @@ long __probe_kernel_read(void *dst, const void *src, size_t size)
 	mm_segment_t old_fs = get_fs();
 
 	set_fs(KERNEL_DS);
-	pagefault_disable();
-	ret = __copy_from_user_inatomic(dst,
-			(__force const void __user *)src, size);
-	pagefault_enable();
+	ret = probe_read_common(dst, (__force const void __user *)src, size);
 	set_fs(old_fs);
 
-	return ret ? -EFAULT : 0;
+	return ret;
 }
 EXPORT_SYMBOL_GPL(probe_kernel_read);
 
+/**
+ * probe_user_read(): safely attempt to read from a user-space location
+ * @dst: pointer to the buffer that shall take the data
+ * @src: address to read from. This must be a user address.
+ * @size: size of the data chunk
+ *
+ * Safely read from user address @src to the buffer at @dst. If a kernel fault
+ * happens, handle that and return -EFAULT.
+ */
+
+long __weak probe_user_read(void *dst, const void __user *src, size_t size)
+    __attribute__((alias("__probe_user_read")));
+
+long __probe_user_read(void *dst, const void __user *src, size_t size)
+{
+	long ret = -EFAULT;
+	mm_segment_t old_fs = get_fs();
+
+	set_fs(USER_DS);
+	if (access_ok(src, size))
+		ret = probe_read_common(dst, src, size);
+	set_fs(old_fs);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(probe_user_read);
+
 /**
  * probe_kernel_write(): safely attempt to write to a location
  * @dst: address to write to
@@ -66,6 +102,7 @@ long __probe_kernel_write(void *dst, const void *src, size_t size)
 }
 EXPORT_SYMBOL_GPL(probe_kernel_write);
 
+
 /**
  * strncpy_from_unsafe: - Copy a NUL terminated string from unsafe address.
  * @dst:   Destination address, in kernel space.  This buffer must be at
@@ -105,3 +142,76 @@ long strncpy_from_unsafe(char *dst, const void *unsafe_addr, long count)
 
 	return ret ? -EFAULT : src - unsafe_addr;
 }
+
+/**
+ * strncpy_from_unsafe_user: - Copy a NUL terminated string from unsafe user
+ *				address.
+ * @dst:   Destination address, in kernel space.  This buffer must be at
+ *         least @count bytes long.
+ * @unsafe_addr: Unsafe user address.
+ * @count: Maximum number of bytes to copy, including the trailing NUL.
+ *
+ * Copies a NUL-terminated string from unsafe user address to kernel buffer.
+ *
+ * On success, returns the length of the string INCLUDING the trailing NUL.
+ *
+ * If access fails, returns -EFAULT (some data may have been copied
+ * and the trailing NUL added).
+ *
+ * If @count is smaller than the length of the string, copies @count-1 bytes,
+ * sets the last byte of @dst buffer to NUL and returns @count.
+ */
+long strncpy_from_unsafe_user(char *dst, const void __user *unsafe_addr,
+			      long count)
+{
+	mm_segment_t old_fs = get_fs();
+	long ret;
+
+	if (unlikely(count <= 0))
+		return 0;
+
+	set_fs(USER_DS);
+	pagefault_disable();
+	ret = strncpy_from_user(dst, unsafe_addr, count);
+	pagefault_enable();
+	set_fs(old_fs);
+
+	if (ret >= count) {
+		ret = count;
+		dst[ret - 1] = '\0';
+	} else if (ret > 0) {
+		ret++;
+	}
+
+	return ret;
+}
+
+/**
+ * strnlen_unsafe_user: - Get the size of a user string INCLUDING final NUL.
+ * @unsafe_addr: The string to measure.
+ * @count: Maximum count (including NUL)
+ *
+ * Get the size of a NUL-terminated string in user space without pagefault.
+ *
+ * Returns the size of the string INCLUDING the terminating NUL.
+ *
+ * If the string is too long, returns a number larger than @count. User
+ * has to check the return value against "> count".
+ * On exception (or invalid count), returns 0.
+ *
+ * Unlike strnlen_user, this can be used from IRQ handler etc. because
+ * it disables pagefaults.
+ */
+long strnlen_unsafe_user(const void __user *unsafe_addr, long count)
+{
+	mm_segment_t old_fs = get_fs();
+	int ret;
+
+	set_fs(USER_DS);
+	pagefault_disable();
+	ret = strnlen_user(unsafe_addr, count);
+	pagefault_enable();
+	set_fs(old_fs);
+
+	return ret;
+}


  parent reply index

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-05-15  5:37 [PATCH -tip v9 0/6] tracing/probes: uaccess: Add support user-space access Masami Hiramatsu
2019-05-15  5:38 ` [PATCH -tip v9 1/6] x86/uaccess: Allow access_ok() in irq context if pagefault_disabled Masami Hiramatsu
2019-05-15  5:38 ` Masami Hiramatsu [this message]
2019-05-15  5:38 ` [PATCH -tip v9 3/6] tracing/probe: Add ustring type for user-space string Masami Hiramatsu
2019-05-15  5:38 ` [PATCH -tip v9 4/6] tracing/probe: Support user-space dereference Masami Hiramatsu
2019-05-15  5:38 ` [PATCH -tip v9 5/6] selftests/ftrace: Add user-memory access syntax testcase Masami Hiramatsu
2019-05-15  5:39 ` [PATCH -tip v9 6/6] perf-probe: Add user memory access attribute support Masami Hiramatsu
2019-05-15  5:55 ` [PATCH -tip v9 0/6] tracing/probes: uaccess: Add support user-space access Ingo Molnar
2019-05-15  8:49   ` Masami Hiramatsu
2019-05-20 15:26   ` Steven Rostedt
2019-05-21  8:28     ` Ingo Molnar
2019-05-21 12:57       ` Steven Rostedt
2019-05-21 15:57         ` Masami Hiramatsu

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=155789869802.26965.4940338412595759063.stgit@devnote2 \
    --to=mhiramat@kernel.org \
    --cc=acme@kernel.org \
    --cc=akpm@linux-foundation.org \
    --cc=alexei.starovoitov@gmail.com \
    --cc=changbin.du@gmail.com \
    --cc=jannh@google.com \
    --cc=joel@joelfernandes.org \
    --cc=keescook@chromium.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=luto@amacapital.net \
    --cc=luto@kernel.org \
    --cc=mingo@kernel.org \
    --cc=namit@vmware.com \
    --cc=peterz@infradead.org \
    --cc=rostedt@goodmis.org \
    --cc=shuah@kernel.org \
    --cc=torvalds@linux-foundation.org \
    --cc=yhs@fb.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

LKML Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/lkml/0 lkml/git/0.git
	git clone --mirror https://lore.kernel.org/lkml/1 lkml/git/1.git
	git clone --mirror https://lore.kernel.org/lkml/2 lkml/git/2.git
	git clone --mirror https://lore.kernel.org/lkml/3 lkml/git/3.git
	git clone --mirror https://lore.kernel.org/lkml/4 lkml/git/4.git
	git clone --mirror https://lore.kernel.org/lkml/5 lkml/git/5.git
	git clone --mirror https://lore.kernel.org/lkml/6 lkml/git/6.git
	git clone --mirror https://lore.kernel.org/lkml/7 lkml/git/7.git
	git clone --mirror https://lore.kernel.org/lkml/8 lkml/git/8.git
	git clone --mirror https://lore.kernel.org/lkml/9 lkml/git/9.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 lkml lkml/ https://lore.kernel.org/lkml \
		linux-kernel@vger.kernel.org
	public-inbox-index lkml

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.linux-kernel


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git