[PATCH v2 0/4] lib: introduce copy_struct_from_user() helper

[PATCH v2 0/4] lib: introduce copy_struct_from_user() helper

[Aleksa Sarai]

Patch changelog:
 v2:
  * Switch to less buggy handling of alignment. [Linus Torvalds, Al Viro]
  * Move is_zeroed_user() to lib/usercopy.c. [kbuild test robot]
  * Move copy_struct_to_user() to lib/usercopy.c. [Christian Brauner]
  * Add self-tests for is_zeroed_user() to lib/test_user_copy.c.
    [Christian Brauner]
 v1: <https://lore.kernel.org/lkml/20190925165915.8135-1-cyphar@cyphar.com/>

This series was split off from the openat2(2) syscall discussion[1].
However, the copy_struct_to_user() helper has been dropped, because
after some discussion it appears that there is no really obvious
semantics for how copy_struct_to_user() should work on mixed-vintages
(for instance, whether [2] is the correct semantics for all syscalls).

A common pattern for syscall extensions is increasing the size of a
struct passed from userspace, such that the zero-value of the new fields
result in the old kernel behaviour (allowing for a mix of userspace and
kernel vintages to operate on one another in most cases).

Previously there was no common lib/ function that implemented
the necessary extension-checking semantics (and different syscalls
implemented them slightly differently or incompletely[3]). This series
implements the helper and ports several syscalls to use it.

[1]: https://lore.kernel.org/lkml/20190904201933.10736-1-cyphar@cyphar.com/

[2]: commit 1251201c0d34 ("sched/core: Fix uclamp ABI bug, clean up and
     robustify sched_read_attr() ABI logic and code")

[3]: For instance {sched_setattr,perf_event_open,clone3}(2) all do do
     similar checks to copy_struct_from_user() while rt_sigprocmask(2)
     always rejects differently-sized struct arguments.

Aleksa Sarai (4):
  lib: introduce copy_struct_from_user() helper
  clone3: switch to copy_struct_from_user()
  sched_setattr: switch to copy_struct_from_user()
  perf_event_open: switch to copy_struct_from_user()

 include/linux/bitops.h     |   7 +++
 include/linux/uaccess.h    |   4 ++
 include/uapi/linux/sched.h |   2 +
 kernel/events/core.c       |  47 +++------------
 kernel/fork.c              |  34 +++--------
 kernel/sched/core.c        |  43 +++-----------
 lib/strnlen_user.c         |   8 +--
 lib/test_user_copy.c       |  59 +++++++++++++++++--
 lib/usercopy.c             | 115 +++++++++++++++++++++++++++++++++++++
 9 files changed, 205 insertions(+), 114 deletions(-)

-- 
2.23.0

[PATCH v2 1/4] lib: introduce copy_struct_from_user() helper

[Aleksa Sarai]

A common pattern for syscall extensions is increasing the size of a
struct passed from userspace, such that the zero-value of the new fields
result in the old kernel behaviour (allowing for a mix of userspace and
kernel vintages to operate on one another in most cases).

While this interface exists for communication in both directions, only
one interface is straightforward to have reasonable semantics for
(userspace passing a struct to the kernel). For kernel returns to
userspace, what the correct semantics are (whether there should be an
error if userspace is unaware of a new extension) is very
syscall-dependent and thus probably cannot be unified between syscalls
(a good example of this problem is [1]).

Previously there was no common lib/ function that implemented
the necessary extension-checking semantics (and different syscalls
implemented them slightly differently or incompletely[2]). Future
patches replace common uses of this pattern to make use of
copy_struct_from_user().

Some in-kernel selftests that insure that the handling of alignment and
various byte patterns are all handled identically to memchr_inv() usage.

[1]: commit 1251201c0d34 ("sched/core: Fix uclamp ABI bug, clean up and
     robustify sched_read_attr() ABI logic and code")

[2]: For instance {sched_setattr,perf_event_open,clone3}(2) all do do
     similar checks to copy_struct_from_user() while rt_sigprocmask(2)
     always rejects differently-sized struct arguments.

Suggested-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>
---
 include/linux/bitops.h  |   7 +++
 include/linux/uaccess.h |   4 ++
 lib/strnlen_user.c      |   8 +--
 lib/test_user_copy.c    |  59 ++++++++++++++++++---
 lib/usercopy.c          | 115 ++++++++++++++++++++++++++++++++++++++++
 5 files changed, 180 insertions(+), 13 deletions(-)

diff --git a/include/linux/bitops.h b/include/linux/bitops.h
index cf074bce3eb3..a23f4c054768 100644
--- a/include/linux/bitops.h
+++ b/include/linux/bitops.h
@@ -4,6 +4,13 @@
 #include <asm/types.h>
 #include <linux/bits.h>
 
+/* Set bits in the first 'n' bytes when loaded from memory */
+#ifdef __LITTLE_ENDIAN
+#  define aligned_byte_mask(n) ((1ul << 8*(n))-1)
+#else
+#  define aligned_byte_mask(n) (~0xfful << (BITS_PER_LONG - 8 - 8*(n)))
+#endif
+
 #define BITS_PER_TYPE(type) (sizeof(type) * BITS_PER_BYTE)
 #define BITS_TO_LONGS(nr)	DIV_ROUND_UP(nr, BITS_PER_TYPE(long))
 
diff --git a/include/linux/uaccess.h b/include/linux/uaccess.h
index 34a038563d97..824569e309e4 100644
--- a/include/linux/uaccess.h
+++ b/include/linux/uaccess.h
@@ -230,6 +230,10 @@ static inline unsigned long __copy_from_user_inatomic_nocache(void *to,
 
 #endif		/* ARCH_HAS_NOCACHE_UACCESS */
 
+extern int is_zeroed_user(const void __user *from, size_t count);
+extern int copy_struct_from_user(void *dst, size_t ksize,
+				 const void __user *src, size_t usize);
+
 /*
  * probe_kernel_read(): safely attempt to read from a location
  * @dst: pointer to the buffer that shall take the data
diff --git a/lib/strnlen_user.c b/lib/strnlen_user.c
index 7f2db3fe311f..39d588aaa8cd 100644
--- a/lib/strnlen_user.c
+++ b/lib/strnlen_user.c
@@ -2,16 +2,10 @@
 #include <linux/kernel.h>
 #include <linux/export.h>
 #include <linux/uaccess.h>
+#include <linux/bitops.h>
 
 #include <asm/word-at-a-time.h>
 
-/* Set bits in the first 'n' bytes when loaded from memory */
-#ifdef __LITTLE_ENDIAN
-#  define aligned_byte_mask(n) ((1ul << 8*(n))-1)
-#else
-#  define aligned_byte_mask(n) (~0xfful << (BITS_PER_LONG - 8 - 8*(n)))
-#endif
-
 /*
  * Do a strnlen, return length of string *with* final '\0'.
  * 'count' is the user-supplied count, while 'max' is the
diff --git a/lib/test_user_copy.c b/lib/test_user_copy.c
index 67bcd5dfd847..f7cde3845ccc 100644
--- a/lib/test_user_copy.c
+++ b/lib/test_user_copy.c
@@ -31,14 +31,58 @@
 # define TEST_U64
 #endif
 
-#define test(condition, msg)		\
-({					\
-	int cond = (condition);		\
-	if (cond)			\
-		pr_warn("%s\n", msg);	\
-	cond;				\
+#define test(condition, msg, ...)					\
+({									\
+	int cond = (condition);						\
+	if (cond)							\
+		pr_warn("[%d] " msg "\n", __LINE__, ##__VA_ARGS__);	\
+	cond;								\
 })
 
+static int test_is_zeroed_user(char *kmem, char __user *umem, size_t size)
+{
+	int ret = 0;
+	size_t start, end, i;
+	size_t zero_start = size / 4;
+	size_t zero_end = size - zero_start;
+
+	/*
+	 * We conduct a series of is_zeroed_user() tests on a block of memory
+	 * with the following byte-pattern (trying every possible [start,end]
+	 * pair):
+	 *
+	 *   [ 00 ff 00 ff ... 00 00 00 00 ... ff 00 ff 00 ]
+	 *
+	 * And we verify that is_zeroed_user() acts identically to memchr_inv().
+	 */
+
+	for (i = 0; i < zero_start; i += 2)
+		kmem[i] = 0x00;
+	for (i = 1; i < zero_start; i += 2)
+		kmem[i] = 0xff;
+
+	for (i = zero_end; i < size; i += 2)
+		kmem[i] = 0xff;
+	for (i = zero_end + 1; i < size; i += 2)
+		kmem[i] = 0x00;
+
+	ret |= test(copy_to_user(umem, kmem, size),
+		    "legitimate copy_to_user failed");
+
+	for (start = 0; start <= size; start++) {
+		for (end = start; end <= size; end++) {
+			int retval = is_zeroed_user(umem + start, end - start);
+			int expected = memchr_inv(kmem + start, 0, end - start) == NULL;
+
+			ret |= test(retval != expected,
+				    "is_zeroed_user(=%d) != memchr_inv(=%d) mismatch (start=%lu, end=%lu)",
+				    retval, expected, start, end);
+		}
+	}
+
+	return ret;
+}
+
 static int __init test_user_copy_init(void)
 {
 	int ret = 0;
@@ -106,6 +150,9 @@ static int __init test_user_copy_init(void)
 #endif
 #undef test_legit
 
+	/* Test usage of is_zeroed_user(). */
+	ret |= test_is_zeroed_user(kmem, usermem, PAGE_SIZE);
+
 	/*
 	 * Invalid usage: none of these copies should succeed.
 	 */
diff --git a/lib/usercopy.c b/lib/usercopy.c
index c2bfbcaeb3dc..f795cf0946ad 100644
--- a/lib/usercopy.c
+++ b/lib/usercopy.c
@@ -1,5 +1,6 @@
 // SPDX-License-Identifier: GPL-2.0
 #include <linux/uaccess.h>
+#include <linux/bitops.h>
 
 /* out-of-line parts */
 
@@ -31,3 +32,117 @@ unsigned long _copy_to_user(void __user *to, const void *from, unsigned long n)
 }
 EXPORT_SYMBOL(_copy_to_user);
 #endif
+
+/**
+ * is_zeroed_user: check if a userspace buffer is full of zeros
+ * @from:  Source address, in userspace.
+ * @size: Size of buffer.
+ *
+ * This is effectively shorthand for "memchr_inv(from, 0, size) == NULL" for
+ * userspace addresses. If there are non-zero bytes present then false is
+ * returned, otherwise true is returned.
+ *
+ * Returns:
+ *  * -EFAULT: access to userspace failed.
+ */
+int is_zeroed_user(const void __user *from, size_t size)
+{
+	unsigned long val;
+	uintptr_t align = (uintptr_t) from % sizeof(unsigned long);
+
+	if (unlikely(!size))
+		return true;
+
+	from -= align;
+	size += align;
+
+	if (!user_access_begin(from, size))
+		return -EFAULT;
+
+	unsafe_get_user(val, (unsigned long __user *) from, err_fault);
+	if (align)
+		val &= ~aligned_byte_mask(align);
+
+	while (size > sizeof(unsigned long)) {
+		if (unlikely(val))
+			goto done;
+
+		from += sizeof(unsigned long);
+		size -= sizeof(unsigned long);
+
+		unsafe_get_user(val, (unsigned long __user *) from, err_fault);
+	}
+
+	if (size < sizeof(unsigned long))
+		val &= aligned_byte_mask(size);
+
+done:
+	user_access_end();
+	return (val == 0);
+err_fault:
+	user_access_end();
+	return -EFAULT;
+}
+EXPORT_SYMBOL(is_zeroed_user);
+
+/**
+ * copy_struct_from_user: copy a struct from userspace
+ * @dst:   Destination address, in kernel space. This buffer must be @ksize
+ *         bytes long.
+ * @ksize: Size of @dst struct.
+ * @src:   Source address, in userspace.
+ * @usize: (Alleged) size of @src struct.
+ *
+ * Copies a struct from userspace to kernel space, in a way that guarantees
+ * backwards-compatibility for struct syscall arguments (as long as future
+ * struct extensions are made such that all new fields are *appended* to the
+ * old struct, and zeroed-out new fields have the same meaning as the old
+ * struct).
+ *
+ * @ksize is just sizeof(*dst), and @usize should've been passed by userspace.
+ * The recommended usage is something like the following:
+ *
+ *   SYSCALL_DEFINE2(foobar, const struct foo __user *, uarg, size_t, usize)
+ *   {
+ *      int err;
+ *      struct foo karg = {};
+ *
+ *      err = copy_struct_from_user(&karg, sizeof(karg), uarg, size);
+ *      if (err)
+ *        return err;
+ *
+ *      // ...
+ *   }
+ *
+ * There are three cases to consider:
+ *  * If @usize == @ksize, then it's copied verbatim.
+ *  * If @usize < @ksize, then the userspace has passed an old struct to a
+ *    newer kernel. The rest of the trailing bytes in @dst (@ksize - @usize)
+ *    are to be zero-filled.
+ *  * If @usize > @ksize, then the userspace has passed a new struct to an
+ *    older kernel. The trailing bytes unknown to the kernel (@usize - @ksize)
+ *    are checked to ensure they are zeroed, otherwise -E2BIG is returned.
+ *
+ * Returns (in all cases, some data may have been copied):
+ *  * -E2BIG:  (@usize > @ksize) and there are non-zero trailing bytes in @src.
+ *  * -EFAULT: access to userspace failed.
+ */
+int copy_struct_from_user(void *dst, size_t ksize,
+			  const void __user *src, size_t usize)
+{
+	size_t size = min(ksize, usize);
+	size_t rest = max(ksize, usize) - size;
+
+	/* Deal with trailing bytes. */
+	if (usize < ksize) {
+		memset(dst + size, 0, rest);
+	} else if (usize > ksize) {
+		int ret = is_zeroed_user(src + size, rest);
+		if (ret <= 0)
+			return ret ?: -E2BIG;
+	}
+	/* Copy the interoperable parts of the struct. */
+	if (copy_from_user(dst, src, size))
+		return -EFAULT;
+	return 0;
+}
-- 
2.23.0

[PATCH v2 2/4] clone3: switch to copy_struct_from_user()

[Aleksa Sarai]

The change is very straightforward, and helps unify the syscall
interface for struct-from-userspace syscalls. Additionally, explicitly
define CLONE_ARGS_SIZE_VER0 to match the other users of the
struct-extension pattern.

Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>
---
 include/uapi/linux/sched.h |  2 ++
 kernel/fork.c              | 34 +++++++---------------------------
 2 files changed, 9 insertions(+), 27 deletions(-)

diff --git a/include/uapi/linux/sched.h b/include/uapi/linux/sched.h
index b3105ac1381a..0945805982b4 100644
--- a/include/uapi/linux/sched.h
+++ b/include/uapi/linux/sched.h
@@ -47,6 +47,8 @@ struct clone_args {
 	__aligned_u64 tls;
 };
 
+#define CLONE_ARGS_SIZE_VER0 64 /* sizeof first published struct */
+
 /*
  * Scheduling policies
  */
diff --git a/kernel/fork.c b/kernel/fork.c
index 541fd805fb88..a86e3841ee4e 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -2530,39 +2530,19 @@ SYSCALL_DEFINE5(clone, unsigned long, clone_flags, unsigned long, newsp,
 #ifdef __ARCH_WANT_SYS_CLONE3
 noinline static int copy_clone_args_from_user(struct kernel_clone_args *kargs,
 					      struct clone_args __user *uargs,
-					      size_t size)
+					      size_t usize)
 {
+	int err;
 	struct clone_args args;
 
-	if (unlikely(size > PAGE_SIZE))
+	if (unlikely(usize > PAGE_SIZE))
 		return -E2BIG;
-
-	if (unlikely(size < sizeof(struct clone_args)))
+	if (unlikely(usize < CLONE_ARGS_SIZE_VER0))
 		return -EINVAL;
 
-	if (unlikely(!access_ok(uargs, size)))
-		return -EFAULT;
-
-	if (size > sizeof(struct clone_args)) {
-		unsigned char __user *addr;
-		unsigned char __user *end;
-		unsigned char val;
-
-		addr = (void __user *)uargs + sizeof(struct clone_args);
-		end = (void __user *)uargs + size;
-
-		for (; addr < end; addr++) {
-			if (get_user(val, addr))
-				return -EFAULT;
-			if (val)
-				return -E2BIG;
-		}
-
-		size = sizeof(struct clone_args);
-	}
-
-	if (copy_from_user(&args, uargs, size))
-		return -EFAULT;
+	err = copy_struct_from_user(&args, sizeof(args), uargs, usize);
+	if (err)
+		return err;
 
 	/*
 	 * Verify that higher 32bits of exit_signal are unset and that
-- 
2.23.0

[PATCH v2 3/4] sched_setattr: switch to copy_struct_from_user()

[Aleksa Sarai]

The change is very straightforward, and helps unify the syscall
interface for struct-from-userspace syscalls. Ideally we could also
unify sched_getattr(2)-style syscalls as well, but unfortunately the
correct semantics for such syscalls are much less clear (see [1] for
more detail). In future we could come up with a more sane idea for how
the syscall interface should look.

[1]: commit 1251201c0d34 ("sched/core: Fix uclamp ABI bug, clean up and
     robustify sched_read_attr() ABI logic and code")

Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>
---
 kernel/sched/core.c | 43 +++++++------------------------------------
 1 file changed, 7 insertions(+), 36 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index df9f1fe5689b..cdb2f5e29b88 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -4900,9 +4900,6 @@ static int sched_copy_attr(struct sched_attr __user *uattr, struct sched_attr *a
 	u32 size;
 	int ret;
 
-	if (!access_ok(uattr, SCHED_ATTR_SIZE_VER0))
-		return -EFAULT;
-
 	/* Zero the full structure, so that a short copy will be nice: */
 	memset(attr, 0, sizeof(*attr));
 
@@ -4910,45 +4907,19 @@ static int sched_copy_attr(struct sched_attr __user *uattr, struct sched_attr *a
 	if (ret)
 		return ret;
 
-	/* Bail out on silly large: */
-	if (size > PAGE_SIZE)
-		goto err_size;
-
 	/* ABI compatibility quirk: */
 	if (!size)
 		size = SCHED_ATTR_SIZE_VER0;
-
-	if (size < SCHED_ATTR_SIZE_VER0)
+	if (size < SCHED_ATTR_SIZE_VER0 || size > PAGE_SIZE)
 		goto err_size;
 
-	/*
-	 * If we're handed a bigger struct than we know of,
-	 * ensure all the unknown bits are 0 - i.e. new
-	 * user-space does not rely on any kernel feature
-	 * extensions we dont know about yet.
-	 */
-	if (size > sizeof(*attr)) {
-		unsigned char __user *addr;
-		unsigned char __user *end;
-		unsigned char val;
-
-		addr = (void __user *)uattr + sizeof(*attr);
-		end  = (void __user *)uattr + size;
-
-		for (; addr < end; addr++) {
-			ret = get_user(val, addr);
-			if (ret)
-				return ret;
-			if (val)
-				goto err_size;
-		}
-		size = sizeof(*attr);
+	ret = copy_struct_from_user(attr, sizeof(*attr), uattr, size);
+	if (ret) {
+		if (ret == -E2BIG)
+			goto err_size;
+		return ret;
 	}
 
-	ret = copy_from_user(attr, uattr, size);
-	if (ret)
-		return -EFAULT;
-
 	if ((attr->sched_flags & SCHED_FLAG_UTIL_CLAMP) &&
 	    size < SCHED_ATTR_SIZE_VER1)
 		return -EINVAL;
@@ -5148,7 +5119,7 @@ sched_attr_copy_to_user(struct sched_attr __user *uattr,
  * sys_sched_getattr - similar to sched_getparam, but with sched_attr
  * @pid: the pid in question.
  * @uattr: structure containing the extended parameters.
- * @usize: sizeof(attr) that user-space knows about, for forwards and backwards compatibility.
+ * @usize: sizeof(attr) for fwd/bwd comp.
  * @flags: for future extension.
  */
 SYSCALL_DEFINE4(sched_getattr, pid_t, pid, struct sched_attr __user *, uattr,
-- 
2.23.0

[PATCH v2 4/4] perf_event_open: switch to copy_struct_from_user()

[Aleksa Sarai]

The change is very straightforward, and helps unify the syscall
interface for struct-from-userspace syscalls.

Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>
---
 kernel/events/core.c | 47 +++++++++-----------------------------------
 1 file changed, 9 insertions(+), 38 deletions(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 0463c1151bae..038ed126bc1b 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -10498,55 +10498,26 @@ static int perf_copy_attr(struct perf_event_attr __user *uattr,
 	u32 size;
 	int ret;
 
-	if (!access_ok(uattr, PERF_ATTR_SIZE_VER0))
-		return -EFAULT;
-
-	/*
-	 * zero the full structure, so that a short copy will be nice.
-	 */
+	/* Zero the full structure, so that a short copy will be nice. */
 	memset(attr, 0, sizeof(*attr));
 
 	ret = get_user(size, &uattr->size);
 	if (ret)
 		return ret;
 
-	if (size > PAGE_SIZE)	/* silly large */
-		goto err_size;
-
-	if (!size)		/* abi compat */
+	/* ABI compatibility quirk: */
+	if (!size)
 		size = PERF_ATTR_SIZE_VER0;
-
-	if (size < PERF_ATTR_SIZE_VER0)
+	if (size < PERF_ATTR_SIZE_VER0 || size > PAGE_SIZE)
 		goto err_size;
 
-	/*
-	 * If we're handed a bigger struct than we know of,
-	 * ensure all the unknown bits are 0 - i.e. new
-	 * user-space does not rely on any kernel feature
-	 * extensions we dont know about yet.
-	 */
-	if (size > sizeof(*attr)) {
-		unsigned char __user *addr;
-		unsigned char __user *end;
-		unsigned char val;
-
-		addr = (void __user *)uattr + sizeof(*attr);
-		end  = (void __user *)uattr + size;
-
-		for (; addr < end; addr++) {
-			ret = get_user(val, addr);
-			if (ret)
-				return ret;
-			if (val)
-				goto err_size;
-		}
-		size = sizeof(*attr);
+	ret = copy_struct_from_user(attr, sizeof(*attr), uattr, size);
+	if (ret) {
+		if (ret == -E2BIG)
+			goto err_size;
+		return ret;
 	}
 
-	ret = copy_from_user(attr, uattr, size);
-	if (ret)
-		return -EFAULT;
-
 	attr->size = size;
 
 	if (attr->__reserved_1)
-- 
2.23.0

Re: [PATCH v2 1/4] lib: introduce copy_struct_from_user() helper

[Aleksa Sarai]

[-- Attachment #1: Type: text/plain, Size: 10795 bytes --]

(Damn, I forgot to add Kees to Cc.)

On 2019-09-26, Aleksa Sarai <cyphar@cyphar.com> wrote:
> A common pattern for syscall extensions is increasing the size of a
> struct passed from userspace, such that the zero-value of the new fields
> result in the old kernel behaviour (allowing for a mix of userspace and
> kernel vintages to operate on one another in most cases).
> 
> While this interface exists for communication in both directions, only
> one interface is straightforward to have reasonable semantics for
> (userspace passing a struct to the kernel). For kernel returns to
> userspace, what the correct semantics are (whether there should be an
> error if userspace is unaware of a new extension) is very
> syscall-dependent and thus probably cannot be unified between syscalls
> (a good example of this problem is [1]).
> 
> Previously there was no common lib/ function that implemented
> the necessary extension-checking semantics (and different syscalls
> implemented them slightly differently or incompletely[2]). Future
> patches replace common uses of this pattern to make use of
> copy_struct_from_user().
> 
> Some in-kernel selftests that insure that the handling of alignment and
> various byte patterns are all handled identically to memchr_inv() usage.
> 
> [1]: commit 1251201c0d34 ("sched/core: Fix uclamp ABI bug, clean up and
>      robustify sched_read_attr() ABI logic and code")
> 
> [2]: For instance {sched_setattr,perf_event_open,clone3}(2) all do do
>      similar checks to copy_struct_from_user() while rt_sigprocmask(2)
>      always rejects differently-sized struct arguments.
> 
> Suggested-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
> Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>
> ---
>  include/linux/bitops.h  |   7 +++
>  include/linux/uaccess.h |   4 ++
>  lib/strnlen_user.c      |   8 +--
>  lib/test_user_copy.c    |  59 ++++++++++++++++++---
>  lib/usercopy.c          | 115 ++++++++++++++++++++++++++++++++++++++++
>  5 files changed, 180 insertions(+), 13 deletions(-)
> 
> diff --git a/include/linux/bitops.h b/include/linux/bitops.h
> index cf074bce3eb3..a23f4c054768 100644
> --- a/include/linux/bitops.h
> +++ b/include/linux/bitops.h
> @@ -4,6 +4,13 @@
>  #include <asm/types.h>
>  #include <linux/bits.h>
>  
> +/* Set bits in the first 'n' bytes when loaded from memory */
> +#ifdef __LITTLE_ENDIAN
> +#  define aligned_byte_mask(n) ((1ul << 8*(n))-1)
> +#else
> +#  define aligned_byte_mask(n) (~0xfful << (BITS_PER_LONG - 8 - 8*(n)))
> +#endif
> +
>  #define BITS_PER_TYPE(type) (sizeof(type) * BITS_PER_BYTE)
>  #define BITS_TO_LONGS(nr)	DIV_ROUND_UP(nr, BITS_PER_TYPE(long))
>  
> diff --git a/include/linux/uaccess.h b/include/linux/uaccess.h
> index 34a038563d97..824569e309e4 100644
> --- a/include/linux/uaccess.h
> +++ b/include/linux/uaccess.h
> @@ -230,6 +230,10 @@ static inline unsigned long __copy_from_user_inatomic_nocache(void *to,
>  
>  #endif		/* ARCH_HAS_NOCACHE_UACCESS */
>  
> +extern int is_zeroed_user(const void __user *from, size_t count);
> +extern int copy_struct_from_user(void *dst, size_t ksize,
> +				 const void __user *src, size_t usize);
> +
>  /*
>   * probe_kernel_read(): safely attempt to read from a location
>   * @dst: pointer to the buffer that shall take the data
> diff --git a/lib/strnlen_user.c b/lib/strnlen_user.c
> index 7f2db3fe311f..39d588aaa8cd 100644
> --- a/lib/strnlen_user.c
> +++ b/lib/strnlen_user.c
> @@ -2,16 +2,10 @@
>  #include <linux/kernel.h>
>  #include <linux/export.h>
>  #include <linux/uaccess.h>
> +#include <linux/bitops.h>
>  
>  #include <asm/word-at-a-time.h>
>  
> -/* Set bits in the first 'n' bytes when loaded from memory */
> -#ifdef __LITTLE_ENDIAN
> -#  define aligned_byte_mask(n) ((1ul << 8*(n))-1)
> -#else
> -#  define aligned_byte_mask(n) (~0xfful << (BITS_PER_LONG - 8 - 8*(n)))
> -#endif
> -
>  /*
>   * Do a strnlen, return length of string *with* final '\0'.
>   * 'count' is the user-supplied count, while 'max' is the
> diff --git a/lib/test_user_copy.c b/lib/test_user_copy.c
> index 67bcd5dfd847..f7cde3845ccc 100644
> --- a/lib/test_user_copy.c
> +++ b/lib/test_user_copy.c
> @@ -31,14 +31,58 @@
>  # define TEST_U64
>  #endif
>  
> -#define test(condition, msg)		\
> -({					\
> -	int cond = (condition);		\
> -	if (cond)			\
> -		pr_warn("%s\n", msg);	\
> -	cond;				\
> +#define test(condition, msg, ...)					\
> +({									\
> +	int cond = (condition);						\
> +	if (cond)							\
> +		pr_warn("[%d] " msg "\n", __LINE__, ##__VA_ARGS__);	\
> +	cond;								\
>  })
>  
> +static int test_is_zeroed_user(char *kmem, char __user *umem, size_t size)
> +{
> +	int ret = 0;
> +	size_t start, end, i;
> +	size_t zero_start = size / 4;
> +	size_t zero_end = size - zero_start;
> +
> +	/*
> +	 * We conduct a series of is_zeroed_user() tests on a block of memory
> +	 * with the following byte-pattern (trying every possible [start,end]
> +	 * pair):
> +	 *
> +	 *   [ 00 ff 00 ff ... 00 00 00 00 ... ff 00 ff 00 ]
> +	 *
> +	 * And we verify that is_zeroed_user() acts identically to memchr_inv().
> +	 */
> +
> +	for (i = 0; i < zero_start; i += 2)
> +		kmem[i] = 0x00;
> +	for (i = 1; i < zero_start; i += 2)
> +		kmem[i] = 0xff;
> +
> +	for (i = zero_end; i < size; i += 2)
> +		kmem[i] = 0xff;
> +	for (i = zero_end + 1; i < size; i += 2)
> +		kmem[i] = 0x00;
> +
> +	ret |= test(copy_to_user(umem, kmem, size),
> +		    "legitimate copy_to_user failed");
> +
> +	for (start = 0; start <= size; start++) {
> +		for (end = start; end <= size; end++) {
> +			int retval = is_zeroed_user(umem + start, end - start);
> +			int expected = memchr_inv(kmem + start, 0, end - start) == NULL;
> +
> +			ret |= test(retval != expected,
> +				    "is_zeroed_user(=%d) != memchr_inv(=%d) mismatch (start=%lu, end=%lu)",
> +				    retval, expected, start, end);
> +		}
> +	}
> +
> +	return ret;
> +}
> +
>  static int __init test_user_copy_init(void)
>  {
>  	int ret = 0;
> @@ -106,6 +150,9 @@ static int __init test_user_copy_init(void)
>  #endif
>  #undef test_legit
>  
> +	/* Test usage of is_zeroed_user(). */
> +	ret |= test_is_zeroed_user(kmem, usermem, PAGE_SIZE);
> +
>  	/*
>  	 * Invalid usage: none of these copies should succeed.
>  	 */
> diff --git a/lib/usercopy.c b/lib/usercopy.c
> index c2bfbcaeb3dc..f795cf0946ad 100644
> --- a/lib/usercopy.c
> +++ b/lib/usercopy.c
> @@ -1,5 +1,6 @@
>  // SPDX-License-Identifier: GPL-2.0
>  #include <linux/uaccess.h>
> +#include <linux/bitops.h>
>  
>  /* out-of-line parts */
>  
> @@ -31,3 +32,117 @@ unsigned long _copy_to_user(void __user *to, const void *from, unsigned long n)
>  }
>  EXPORT_SYMBOL(_copy_to_user);
>  #endif
> +
> +/**
> + * is_zeroed_user: check if a userspace buffer is full of zeros
> + * @from:  Source address, in userspace.
> + * @size: Size of buffer.
> + *
> + * This is effectively shorthand for "memchr_inv(from, 0, size) == NULL" for
> + * userspace addresses. If there are non-zero bytes present then false is
> + * returned, otherwise true is returned.
> + *
> + * Returns:
> + *  * -EFAULT: access to userspace failed.
> + */
> +int is_zeroed_user(const void __user *from, size_t size)
> +{
> +	unsigned long val;
> +	uintptr_t align = (uintptr_t) from % sizeof(unsigned long);
> +
> +	if (unlikely(!size))
> +		return true;
> +
> +	from -= align;
> +	size += align;
> +
> +	if (!user_access_begin(from, size))
> +		return -EFAULT;
> +
> +	unsafe_get_user(val, (unsigned long __user *) from, err_fault);
> +	if (align)
> +		val &= ~aligned_byte_mask(align);
> +
> +	while (size > sizeof(unsigned long)) {
> +		if (unlikely(val))
> +			goto done;
> +
> +		from += sizeof(unsigned long);
> +		size -= sizeof(unsigned long);
> +
> +		unsafe_get_user(val, (unsigned long __user *) from, err_fault);
> +	}
> +
> +	if (size < sizeof(unsigned long))
> +		val &= aligned_byte_mask(size);
> +
> +done:
> +	user_access_end();
> +	return (val == 0);
> +err_fault:
> +	user_access_end();
> +	return -EFAULT;
> +}
> +EXPORT_SYMBOL(is_zeroed_user);
> +
> +/**
> + * copy_struct_from_user: copy a struct from userspace
> + * @dst:   Destination address, in kernel space. This buffer must be @ksize
> + *         bytes long.
> + * @ksize: Size of @dst struct.
> + * @src:   Source address, in userspace.
> + * @usize: (Alleged) size of @src struct.
> + *
> + * Copies a struct from userspace to kernel space, in a way that guarantees
> + * backwards-compatibility for struct syscall arguments (as long as future
> + * struct extensions are made such that all new fields are *appended* to the
> + * old struct, and zeroed-out new fields have the same meaning as the old
> + * struct).
> + *
> + * @ksize is just sizeof(*dst), and @usize should've been passed by userspace.
> + * The recommended usage is something like the following:
> + *
> + *   SYSCALL_DEFINE2(foobar, const struct foo __user *, uarg, size_t, usize)
> + *   {
> + *      int err;
> + *      struct foo karg = {};
> + *
> + *      err = copy_struct_from_user(&karg, sizeof(karg), uarg, size);
> + *      if (err)
> + *        return err;
> + *
> + *      // ...
> + *   }
> + *
> + * There are three cases to consider:
> + *  * If @usize == @ksize, then it's copied verbatim.
> + *  * If @usize < @ksize, then the userspace has passed an old struct to a
> + *    newer kernel. The rest of the trailing bytes in @dst (@ksize - @usize)
> + *    are to be zero-filled.
> + *  * If @usize > @ksize, then the userspace has passed a new struct to an
> + *    older kernel. The trailing bytes unknown to the kernel (@usize - @ksize)
> + *    are checked to ensure they are zeroed, otherwise -E2BIG is returned.
> + *
> + * Returns (in all cases, some data may have been copied):
> + *  * -E2BIG:  (@usize > @ksize) and there are non-zero trailing bytes in @src.
> + *  * -EFAULT: access to userspace failed.
> + */
> +int copy_struct_from_user(void *dst, size_t ksize,
> +			  const void __user *src, size_t usize)
> +{
> +	size_t size = min(ksize, usize);
> +	size_t rest = max(ksize, usize) - size;
> +
> +	/* Deal with trailing bytes. */
> +	if (usize < ksize) {
> +		memset(dst + size, 0, rest);
> +	} else if (usize > ksize) {
> +		int ret = is_zeroed_user(src + size, rest);
> +		if (ret <= 0)
> +			return ret ?: -E2BIG;
> +	}
> +	/* Copy the interoperable parts of the struct. */
> +	if (copy_from_user(dst, src, size))
> +		return -EFAULT;
> +	return 0;
> +}
> -- 
> 2.23.0
> 


-- 
Aleksa Sarai
Senior Software Engineer (Containers)
SUSE Linux GmbH
<https://www.cyphar.com/>

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 228 bytes --]

Re: [PATCH v2 1/4] lib: introduce copy_struct_from_user() helper

[Christian Brauner]

On Thu, Sep 26, 2019 at 01:03:29AM +0200, Aleksa Sarai wrote:
> A common pattern for syscall extensions is increasing the size of a
> struct passed from userspace, such that the zero-value of the new fields
> result in the old kernel behaviour (allowing for a mix of userspace and
> kernel vintages to operate on one another in most cases).
> 
> While this interface exists for communication in both directions, only
> one interface is straightforward to have reasonable semantics for
> (userspace passing a struct to the kernel). For kernel returns to
> userspace, what the correct semantics are (whether there should be an
> error if userspace is unaware of a new extension) is very
> syscall-dependent and thus probably cannot be unified between syscalls
> (a good example of this problem is [1]).
> 
> Previously there was no common lib/ function that implemented
> the necessary extension-checking semantics (and different syscalls
> implemented them slightly differently or incompletely[2]). Future
> patches replace common uses of this pattern to make use of
> copy_struct_from_user().
> 
> Some in-kernel selftests that insure that the handling of alignment and
> various byte patterns are all handled identically to memchr_inv() usage.
> 
> [1]: commit 1251201c0d34 ("sched/core: Fix uclamp ABI bug, clean up and
>      robustify sched_read_attr() ABI logic and code")
> 
> [2]: For instance {sched_setattr,perf_event_open,clone3}(2) all do do
>      similar checks to copy_struct_from_user() while rt_sigprocmask(2)
>      always rejects differently-sized struct arguments.
> 
> Suggested-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
> Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>
> ---
>  include/linux/bitops.h  |   7 +++
>  include/linux/uaccess.h |   4 ++
>  lib/strnlen_user.c      |   8 +--
>  lib/test_user_copy.c    |  59 ++++++++++++++++++---
>  lib/usercopy.c          | 115 ++++++++++++++++++++++++++++++++++++++++
>  5 files changed, 180 insertions(+), 13 deletions(-)
> 
> diff --git a/include/linux/bitops.h b/include/linux/bitops.h
> index cf074bce3eb3..a23f4c054768 100644
> --- a/include/linux/bitops.h
> +++ b/include/linux/bitops.h
> @@ -4,6 +4,13 @@
>  #include <asm/types.h>
>  #include <linux/bits.h>
>  
> +/* Set bits in the first 'n' bytes when loaded from memory */
> +#ifdef __LITTLE_ENDIAN
> +#  define aligned_byte_mask(n) ((1ul << 8*(n))-1)
> +#else
> +#  define aligned_byte_mask(n) (~0xfful << (BITS_PER_LONG - 8 - 8*(n)))
> +#endif
> +
>  #define BITS_PER_TYPE(type) (sizeof(type) * BITS_PER_BYTE)
>  #define BITS_TO_LONGS(nr)	DIV_ROUND_UP(nr, BITS_PER_TYPE(long))
>  
> diff --git a/include/linux/uaccess.h b/include/linux/uaccess.h
> index 34a038563d97..824569e309e4 100644
> --- a/include/linux/uaccess.h
> +++ b/include/linux/uaccess.h
> @@ -230,6 +230,10 @@ static inline unsigned long __copy_from_user_inatomic_nocache(void *to,
>  
>  #endif		/* ARCH_HAS_NOCACHE_UACCESS */
>  
> +extern int is_zeroed_user(const void __user *from, size_t count);
> +extern int copy_struct_from_user(void *dst, size_t ksize,
> +				 const void __user *src, size_t usize);
> +
>  /*
>   * probe_kernel_read(): safely attempt to read from a location
>   * @dst: pointer to the buffer that shall take the data
> diff --git a/lib/strnlen_user.c b/lib/strnlen_user.c
> index 7f2db3fe311f..39d588aaa8cd 100644
> --- a/lib/strnlen_user.c
> +++ b/lib/strnlen_user.c
> @@ -2,16 +2,10 @@
>  #include <linux/kernel.h>
>  #include <linux/export.h>
>  #include <linux/uaccess.h>
> +#include <linux/bitops.h>
>  
>  #include <asm/word-at-a-time.h>
>  
> -/* Set bits in the first 'n' bytes when loaded from memory */
> -#ifdef __LITTLE_ENDIAN
> -#  define aligned_byte_mask(n) ((1ul << 8*(n))-1)
> -#else
> -#  define aligned_byte_mask(n) (~0xfful << (BITS_PER_LONG - 8 - 8*(n)))
> -#endif
> -
>  /*
>   * Do a strnlen, return length of string *with* final '\0'.
>   * 'count' is the user-supplied count, while 'max' is the
> diff --git a/lib/test_user_copy.c b/lib/test_user_copy.c
> index 67bcd5dfd847..f7cde3845ccc 100644
> --- a/lib/test_user_copy.c
> +++ b/lib/test_user_copy.c
> @@ -31,14 +31,58 @@
>  # define TEST_U64
>  #endif
>  
> -#define test(condition, msg)		\
> -({					\
> -	int cond = (condition);		\
> -	if (cond)			\
> -		pr_warn("%s\n", msg);	\
> -	cond;				\
> +#define test(condition, msg, ...)					\
> +({									\
> +	int cond = (condition);						\
> +	if (cond)							\
> +		pr_warn("[%d] " msg "\n", __LINE__, ##__VA_ARGS__);	\
> +	cond;								\
>  })
>  
> +static int test_is_zeroed_user(char *kmem, char __user *umem, size_t size)
> +{
> +	int ret = 0;
> +	size_t start, end, i;
> +	size_t zero_start = size / 4;
> +	size_t zero_end = size - zero_start;
> +
> +	/*
> +	 * We conduct a series of is_zeroed_user() tests on a block of memory
> +	 * with the following byte-pattern (trying every possible [start,end]
> +	 * pair):
> +	 *
> +	 *   [ 00 ff 00 ff ... 00 00 00 00 ... ff 00 ff 00 ]
> +	 *
> +	 * And we verify that is_zeroed_user() acts identically to memchr_inv().
> +	 */
> +
> +	for (i = 0; i < zero_start; i += 2)
> +		kmem[i] = 0x00;
> +	for (i = 1; i < zero_start; i += 2)
> +		kmem[i] = 0xff;
> +
> +	for (i = zero_end; i < size; i += 2)
> +		kmem[i] = 0xff;
> +	for (i = zero_end + 1; i < size; i += 2)
> +		kmem[i] = 0x00;
> +
> +	ret |= test(copy_to_user(umem, kmem, size),
> +		    "legitimate copy_to_user failed");
> +
> +	for (start = 0; start <= size; start++) {
> +		for (end = start; end <= size; end++) {
> +			int retval = is_zeroed_user(umem + start, end - start);
> +			int expected = memchr_inv(kmem + start, 0, end - start) == NULL;
> +
> +			ret |= test(retval != expected,
> +				    "is_zeroed_user(=%d) != memchr_inv(=%d) mismatch (start=%lu, end=%lu)",
> +				    retval, expected, start, end);
> +		}
> +	}
> +
> +	return ret;
> +}
> +
>  static int __init test_user_copy_init(void)
>  {
>  	int ret = 0;
> @@ -106,6 +150,9 @@ static int __init test_user_copy_init(void)
>  #endif
>  #undef test_legit
>  
> +	/* Test usage of is_zeroed_user(). */
> +	ret |= test_is_zeroed_user(kmem, usermem, PAGE_SIZE);
> +
>  	/*
>  	 * Invalid usage: none of these copies should succeed.
>  	 */
> diff --git a/lib/usercopy.c b/lib/usercopy.c
> index c2bfbcaeb3dc..f795cf0946ad 100644
> --- a/lib/usercopy.c
> +++ b/lib/usercopy.c
> @@ -1,5 +1,6 @@
>  // SPDX-License-Identifier: GPL-2.0
>  #include <linux/uaccess.h>
> +#include <linux/bitops.h>
>  
>  /* out-of-line parts */
>  
> @@ -31,3 +32,117 @@ unsigned long _copy_to_user(void __user *to, const void *from, unsigned long n)
>  }
>  EXPORT_SYMBOL(_copy_to_user);
>  #endif
> +
> +/**
> + * is_zeroed_user: check if a userspace buffer is full of zeros
> + * @from:  Source address, in userspace.
> + * @size: Size of buffer.
> + *
> + * This is effectively shorthand for "memchr_inv(from, 0, size) == NULL" for
> + * userspace addresses. If there are non-zero bytes present then false is
> + * returned, otherwise true is returned.
> + *
> + * Returns:
> + *  * -EFAULT: access to userspace failed.
> + */
> +int is_zeroed_user(const void __user *from, size_t size)
> +{
> +	unsigned long val;
> +	uintptr_t align = (uintptr_t) from % sizeof(unsigned long);
> +
> +	if (unlikely(!size))
> +		return true;

You're returning "true" and another implicit boolean with (val == 0)
down below but -EFAULT in other places. But that function is
int is_zeroed_user()
Would probably be good if you either switch to
bool is_zeroed_user()
as the name suggests or rename the function and have it return an int
everywhere.

> +
> +	from -= align;
> +	size += align;
> +
> +	if (!user_access_begin(from, size))
> +		return -EFAULT;
> +
> +	unsafe_get_user(val, (unsigned long __user *) from, err_fault);
> +	if (align)
> +		val &= ~aligned_byte_mask(align);
> +
> +	while (size > sizeof(unsigned long)) {
> +		if (unlikely(val))
> +			goto done;
> +
> +		from += sizeof(unsigned long);
> +		size -= sizeof(unsigned long);
> +
> +		unsafe_get_user(val, (unsigned long __user *) from, err_fault);
> +	}
> +
> +	if (size < sizeof(unsigned long))
> +		val &= aligned_byte_mask(size);
> +
> +done:
> +	user_access_end();
> +	return (val == 0);
> +err_fault:
> +	user_access_end();
> +	return -EFAULT;
> +}
> +EXPORT_SYMBOL(is_zeroed_user);
> +
> +/**
> + * copy_struct_from_user: copy a struct from userspace
> + * @dst:   Destination address, in kernel space. This buffer must be @ksize
> + *         bytes long.
> + * @ksize: Size of @dst struct.
> + * @src:   Source address, in userspace.
> + * @usize: (Alleged) size of @src struct.
> + *
> + * Copies a struct from userspace to kernel space, in a way that guarantees
> + * backwards-compatibility for struct syscall arguments (as long as future
> + * struct extensions are made such that all new fields are *appended* to the
> + * old struct, and zeroed-out new fields have the same meaning as the old
> + * struct).
> + *
> + * @ksize is just sizeof(*dst), and @usize should've been passed by userspace.
> + * The recommended usage is something like the following:
> + *
> + *   SYSCALL_DEFINE2(foobar, const struct foo __user *, uarg, size_t, usize)
> + *   {
> + *      int err;
> + *      struct foo karg = {};
> + *
> + *      err = copy_struct_from_user(&karg, sizeof(karg), uarg, size);
> + *      if (err)
> + *        return err;
> + *
> + *      // ...
> + *   }
> + *
> + * There are three cases to consider:
> + *  * If @usize == @ksize, then it's copied verbatim.
> + *  * If @usize < @ksize, then the userspace has passed an old struct to a
> + *    newer kernel. The rest of the trailing bytes in @dst (@ksize - @usize)
> + *    are to be zero-filled.
> + *  * If @usize > @ksize, then the userspace has passed a new struct to an
> + *    older kernel. The trailing bytes unknown to the kernel (@usize - @ksize)
> + *    are checked to ensure they are zeroed, otherwise -E2BIG is returned.
> + *
> + * Returns (in all cases, some data may have been copied):
> + *  * -E2BIG:  (@usize > @ksize) and there are non-zero trailing bytes in @src.
> + *  * -EFAULT: access to userspace failed.
> + */
> +int copy_struct_from_user(void *dst, size_t ksize,
> +			  const void __user *src, size_t usize)
> +{
> +	size_t size = min(ksize, usize);
> +	size_t rest = max(ksize, usize) - size;
> +
> +	/* Deal with trailing bytes. */
> +	if (usize < ksize) {
> +		memset(dst + size, 0, rest);
> +	} else if (usize > ksize) {
> +		int ret = is_zeroed_user(src + size, rest);
> +		if (ret <= 0)
> +			return ret ?: -E2BIG;
> +	}
> +	/* Copy the interoperable parts of the struct. */
> +	if (copy_from_user(dst, src, size))
> +		return -EFAULT;
> +	return 0;
> +}
> -- 
> 2.23.0
> 

Re: [PATCH v2 1/4] lib: introduce copy_struct_from_user() helper

[kbuild test robot]

[-- Attachment #1: Type: text/plain, Size: 5404 bytes --]

Hi Aleksa,

Thank you for the patch! Perhaps something to improve:

[auto build test WARNING on linus/master]
[cannot apply to v5.3 next-20190924]
[if your patch is applied to the wrong git tree, please drop us a note to help
improve the system. BTW, we also suggest to use '--base' option to specify the
base tree in git format-patch, please see https://stackoverflow.com/a/37406982]

url:    https://github.com/0day-ci/linux/commits/Aleksa-Sarai/lib-introduce-copy_struct_from_user-helper/20190926-071752
config: sh-allmodconfig (attached as .config)
compiler: sh4-linux-gcc (GCC) 7.4.0
reproduce:
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # save the attached .config to linux build tree
        GCC_VERSION=7.4.0 make.cross ARCH=sh 

If you fix the issue, kindly add following tag
Reported-by: kbuild test robot <lkp@intel.com>

All warnings (new ones prefixed by >>):

   In file included from include/linux/printk.h:7:0,
                    from include/linux/kernel.h:15,
                    from include/asm-generic/bug.h:18,
                    from arch/sh/include/asm/bug.h:112,
                    from include/linux/bug.h:5,
                    from include/linux/mmdebug.h:5,
                    from include/linux/mm.h:9,
                    from include/linux/mman.h:5,
                    from lib/test_user_copy.c:13:
   lib/test_user_copy.c: In function 'test_is_zeroed_user':
   include/linux/kern_levels.h:5:18: warning: format '%lu' expects argument of type 'long unsigned int', but argument 5 has type 'size_t {aka unsigned int}' [-Wformat=]
    #define KERN_SOH "\001"  /* ASCII Start Of Header */
                     ^
   include/linux/kern_levels.h:12:22: note: in expansion of macro 'KERN_SOH'
    #define KERN_WARNING KERN_SOH "4" /* warning conditions */
                         ^~~~~~~~
   include/linux/printk.h:306:9: note: in expansion of macro 'KERN_WARNING'
     printk(KERN_WARNING pr_fmt(fmt), ##__VA_ARGS__)
            ^~~~~~~~~~~~
   include/linux/printk.h:307:17: note: in expansion of macro 'pr_warning'
    #define pr_warn pr_warning
                    ^~~~~~~~~~
>> lib/test_user_copy.c:38:3: note: in expansion of macro 'pr_warn'
      pr_warn("[%d] " msg "\n", __LINE__, ##__VA_ARGS__); \
      ^~~~~~~
>> lib/test_user_copy.c:77:11: note: in expansion of macro 'test'
       ret |= test(retval != expected,
              ^~~~
   include/linux/kern_levels.h:5:18: warning: format '%lu' expects argument of type 'long unsigned int', but argument 6 has type 'size_t {aka unsigned int}' [-Wformat=]
    #define KERN_SOH "\001"  /* ASCII Start Of Header */
                     ^
   include/linux/kern_levels.h:12:22: note: in expansion of macro 'KERN_SOH'
    #define KERN_WARNING KERN_SOH "4" /* warning conditions */
                         ^~~~~~~~
   include/linux/printk.h:306:9: note: in expansion of macro 'KERN_WARNING'
     printk(KERN_WARNING pr_fmt(fmt), ##__VA_ARGS__)
            ^~~~~~~~~~~~
   include/linux/printk.h:307:17: note: in expansion of macro 'pr_warning'
    #define pr_warn pr_warning
                    ^~~~~~~~~~
>> lib/test_user_copy.c:38:3: note: in expansion of macro 'pr_warn'
      pr_warn("[%d] " msg "\n", __LINE__, ##__VA_ARGS__); \
      ^~~~~~~
>> lib/test_user_copy.c:77:11: note: in expansion of macro 'test'
       ret |= test(retval != expected,
              ^~~~

vim +/pr_warn +38 lib/test_user_copy.c

    33	
    34	#define test(condition, msg, ...)					\
    35	({									\
    36		int cond = (condition);						\
    37		if (cond)							\
  > 38			pr_warn("[%d] " msg "\n", __LINE__, ##__VA_ARGS__);	\
    39		cond;								\
    40	})
    41	
    42	static int test_is_zeroed_user(char *kmem, char __user *umem, size_t size)
    43	{
    44		int ret = 0;
    45		size_t start, end, i;
    46		size_t zero_start = size / 4;
    47		size_t zero_end = size - zero_start;
    48	
    49		/*
    50		 * We conduct a series of is_zeroed_user() tests on a block of memory
    51		 * with the following byte-pattern (trying every possible [start,end]
    52		 * pair):
    53		 *
    54		 *   [ 00 ff 00 ff ... 00 00 00 00 ... ff 00 ff 00 ]
    55		 *
    56		 * And we verify that is_zeroed_user() acts identically to memchr_inv().
    57		 */
    58	
    59		for (i = 0; i < zero_start; i += 2)
    60			kmem[i] = 0x00;
    61		for (i = 1; i < zero_start; i += 2)
    62			kmem[i] = 0xff;
    63	
    64		for (i = zero_end; i < size; i += 2)
    65			kmem[i] = 0xff;
    66		for (i = zero_end + 1; i < size; i += 2)
    67			kmem[i] = 0x00;
    68	
    69		ret |= test(copy_to_user(umem, kmem, size),
    70			    "legitimate copy_to_user failed");
    71	
    72		for (start = 0; start <= size; start++) {
    73			for (end = start; end <= size; end++) {
    74				int retval = is_zeroed_user(umem + start, end - start);
    75				int expected = memchr_inv(kmem + start, 0, end - start) == NULL;
    76	
  > 77				ret |= test(retval != expected,
    78					    "is_zeroed_user(=%d) != memchr_inv(=%d) mismatch (start=%lu, end=%lu)",
    79					    retval, expected, start, end);
    80			}
    81		}
    82	
    83		return ret;
    84	}
    85	

---
0-DAY kernel test infrastructure                Open Source Technology Center
https://lists.01.org/pipermail/kbuild-all                   Intel Corporation

[-- Attachment #2: .config.gz --]
[-- Type: application/gzip, Size: 52170 bytes --]

Re: [PATCH v2 1/4] lib: introduce copy_struct_from_user() helper

[kbuild test robot]

[-- Attachment #1: Type: text/plain, Size: 5404 bytes --]

Hi Aleksa,

Thank you for the patch! Perhaps something to improve:

[auto build test WARNING on linus/master]
[cannot apply to v5.3 next-20190924]
[if your patch is applied to the wrong git tree, please drop us a note to help
improve the system. BTW, we also suggest to use '--base' option to specify the
base tree in git format-patch, please see https://stackoverflow.com/a/37406982]

url:    https://github.com/0day-ci/linux/commits/Aleksa-Sarai/lib-introduce-copy_struct_from_user-helper/20190926-071752
config: sh-allmodconfig (attached as .config)
compiler: sh4-linux-gcc (GCC) 7.4.0
reproduce:
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # save the attached .config to linux build tree
        GCC_VERSION=7.4.0 make.cross ARCH=sh 

If you fix the issue, kindly add following tag
Reported-by: kbuild test robot <lkp@intel.com>

All warnings (new ones prefixed by >>):

   In file included from include/linux/printk.h:7:0,
                    from include/linux/kernel.h:15,
                    from include/asm-generic/bug.h:18,
                    from arch/sh/include/asm/bug.h:112,
                    from include/linux/bug.h:5,
                    from include/linux/mmdebug.h:5,
                    from include/linux/mm.h:9,
                    from include/linux/mman.h:5,
                    from lib/test_user_copy.c:13:
   lib/test_user_copy.c: In function 'test_is_zeroed_user':
   include/linux/kern_levels.h:5:18: warning: format '%lu' expects argument of type 'long unsigned int', but argument 5 has type 'size_t {aka unsigned int}' [-Wformat=]
    #define KERN_SOH "\001"  /* ASCII Start Of Header */
                     ^
   include/linux/kern_levels.h:12:22: note: in expansion of macro 'KERN_SOH'
    #define KERN_WARNING KERN_SOH "4" /* warning conditions */
                         ^~~~~~~~
   include/linux/printk.h:306:9: note: in expansion of macro 'KERN_WARNING'
     printk(KERN_WARNING pr_fmt(fmt), ##__VA_ARGS__)
            ^~~~~~~~~~~~
   include/linux/printk.h:307:17: note: in expansion of macro 'pr_warning'
    #define pr_warn pr_warning
                    ^~~~~~~~~~
>> lib/test_user_copy.c:38:3: note: in expansion of macro 'pr_warn'
      pr_warn("[%d] " msg "\n", __LINE__, ##__VA_ARGS__); \
      ^~~~~~~
>> lib/test_user_copy.c:77:11: note: in expansion of macro 'test'
       ret |= test(retval != expected,
              ^~~~
   include/linux/kern_levels.h:5:18: warning: format '%lu' expects argument of type 'long unsigned int', but argument 6 has type 'size_t {aka unsigned int}' [-Wformat=]
    #define KERN_SOH "\001"  /* ASCII Start Of Header */
                     ^
   include/linux/kern_levels.h:12:22: note: in expansion of macro 'KERN_SOH'
    #define KERN_WARNING KERN_SOH "4" /* warning conditions */
                         ^~~~~~~~
   include/linux/printk.h:306:9: note: in expansion of macro 'KERN_WARNING'
     printk(KERN_WARNING pr_fmt(fmt), ##__VA_ARGS__)
            ^~~~~~~~~~~~
   include/linux/printk.h:307:17: note: in expansion of macro 'pr_warning'
    #define pr_warn pr_warning
                    ^~~~~~~~~~
>> lib/test_user_copy.c:38:3: note: in expansion of macro 'pr_warn'
      pr_warn("[%d] " msg "\n", __LINE__, ##__VA_ARGS__); \
      ^~~~~~~
>> lib/test_user_copy.c:77:11: note: in expansion of macro 'test'
       ret |= test(retval != expected,
              ^~~~

vim +/pr_warn +38 lib/test_user_copy.c

    33	
    34	#define test(condition, msg, ...)					\
    35	({									\
    36		int cond = (condition);						\
    37		if (cond)							\
  > 38			pr_warn("[%d] " msg "\n", __LINE__, ##__VA_ARGS__);	\
    39		cond;								\
    40	})
    41	
    42	static int test_is_zeroed_user(char *kmem, char __user *umem, size_t size)
    43	{
    44		int ret = 0;
    45		size_t start, end, i;
    46		size_t zero_start = size / 4;
    47		size_t zero_end = size - zero_start;
    48	
    49		/*
    50		 * We conduct a series of is_zeroed_user() tests on a block of memory
    51		 * with the following byte-pattern (trying every possible [start,end]
    52		 * pair):
    53		 *
    54		 *   [ 00 ff 00 ff ... 00 00 00 00 ... ff 00 ff 00 ]
    55		 *
    56		 * And we verify that is_zeroed_user() acts identically to memchr_inv().
    57		 */
    58	
    59		for (i = 0; i < zero_start; i += 2)
    60			kmem[i] = 0x00;
    61		for (i = 1; i < zero_start; i += 2)
    62			kmem[i] = 0xff;
    63	
    64		for (i = zero_end; i < size; i += 2)
    65			kmem[i] = 0xff;
    66		for (i = zero_end + 1; i < size; i += 2)
    67			kmem[i] = 0x00;
    68	
    69		ret |= test(copy_to_user(umem, kmem, size),
    70			    "legitimate copy_to_user failed");
    71	
    72		for (start = 0; start <= size; start++) {
    73			for (end = start; end <= size; end++) {
    74				int retval = is_zeroed_user(umem + start, end - start);
    75				int expected = memchr_inv(kmem + start, 0, end - start) == NULL;
    76	
  > 77				ret |= test(retval != expected,
    78					    "is_zeroed_user(=%d) != memchr_inv(=%d) mismatch (start=%lu, end=%lu)",
    79					    retval, expected, start, end);
    80			}
    81		}
    82	
    83		return ret;
    84	}
    85	

---
0-DAY kernel test infrastructure                Open Source Technology Center
https://lists.01.org/pipermail/kbuild-all                   Intel Corporation

[-- Attachment #2: .config.gz --]
[-- Type: application/gzip, Size: 52170 bytes --]

Re: [PATCH v2 1/4] lib: introduce copy_struct_from_user() helper

[Christian Brauner]

On Thu, Sep 26, 2019 at 01:03:29AM +0200, Aleksa Sarai wrote:
> A common pattern for syscall extensions is increasing the size of a
> struct passed from userspace, such that the zero-value of the new fields
> result in the old kernel behaviour (allowing for a mix of userspace and
> kernel vintages to operate on one another in most cases).
> 
> While this interface exists for communication in both directions, only
> one interface is straightforward to have reasonable semantics for
> (userspace passing a struct to the kernel). For kernel returns to
> userspace, what the correct semantics are (whether there should be an
> error if userspace is unaware of a new extension) is very
> syscall-dependent and thus probably cannot be unified between syscalls
> (a good example of this problem is [1]).
> 
> Previously there was no common lib/ function that implemented
> the necessary extension-checking semantics (and different syscalls
> implemented them slightly differently or incompletely[2]). Future
> patches replace common uses of this pattern to make use of
> copy_struct_from_user().
> 
> Some in-kernel selftests that insure that the handling of alignment and
> various byte patterns are all handled identically to memchr_inv() usage.
> 
> [1]: commit 1251201c0d34 ("sched/core: Fix uclamp ABI bug, clean up and
>      robustify sched_read_attr() ABI logic and code")
> 
> [2]: For instance {sched_setattr,perf_event_open,clone3}(2) all do do
>      similar checks to copy_struct_from_user() while rt_sigprocmask(2)
>      always rejects differently-sized struct arguments.
> 
> Suggested-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
> Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>
> ---
>  include/linux/bitops.h  |   7 +++
>  include/linux/uaccess.h |   4 ++
>  lib/strnlen_user.c      |   8 +--
>  lib/test_user_copy.c    |  59 ++++++++++++++++++---
>  lib/usercopy.c          | 115 ++++++++++++++++++++++++++++++++++++++++
>  5 files changed, 180 insertions(+), 13 deletions(-)
> 
> diff --git a/include/linux/bitops.h b/include/linux/bitops.h
> index cf074bce3eb3..a23f4c054768 100644
> --- a/include/linux/bitops.h
> +++ b/include/linux/bitops.h
> @@ -4,6 +4,13 @@
>  #include <asm/types.h>
>  #include <linux/bits.h>
>  
> +/* Set bits in the first 'n' bytes when loaded from memory */
> +#ifdef __LITTLE_ENDIAN
> +#  define aligned_byte_mask(n) ((1ul << 8*(n))-1)
> +#else
> +#  define aligned_byte_mask(n) (~0xfful << (BITS_PER_LONG - 8 - 8*(n)))
> +#endif

Nti: The style in bitops.h suggestes this should be:

+/* Set bits in the first 'n' bytes when loaded from memory */
+#ifdef __LITTLE_ENDIAN
+#  define aligned_byte_mask(n) ((1UL << 8*(n))-1)
+#else
+#  define aligned_byte_mask(n) (~0xffUL << (BITS_PER_LONG - 8 - 8*(n)))
+#endif

Using UL also makes 0xffUL clearer.

> +
>  #define BITS_PER_TYPE(type) (sizeof(type) * BITS_PER_BYTE)
>  #define BITS_TO_LONGS(nr)	DIV_ROUND_UP(nr, BITS_PER_TYPE(long))
>  
> diff --git a/include/linux/uaccess.h b/include/linux/uaccess.h
> index 34a038563d97..824569e309e4 100644
> --- a/include/linux/uaccess.h
> +++ b/include/linux/uaccess.h
> @@ -230,6 +230,10 @@ static inline unsigned long __copy_from_user_inatomic_nocache(void *to,
>  
>  #endif		/* ARCH_HAS_NOCACHE_UACCESS */
>  
> +extern int is_zeroed_user(const void __user *from, size_t count);
> +extern int copy_struct_from_user(void *dst, size_t ksize,
> +				 const void __user *src, size_t usize);
> +
>  /*
>   * probe_kernel_read(): safely attempt to read from a location
>   * @dst: pointer to the buffer that shall take the data
> diff --git a/lib/strnlen_user.c b/lib/strnlen_user.c
> index 7f2db3fe311f..39d588aaa8cd 100644
> --- a/lib/strnlen_user.c
> +++ b/lib/strnlen_user.c
> @@ -2,16 +2,10 @@
>  #include <linux/kernel.h>
>  #include <linux/export.h>
>  #include <linux/uaccess.h>
> +#include <linux/bitops.h>
>  
>  #include <asm/word-at-a-time.h>
>  
> -/* Set bits in the first 'n' bytes when loaded from memory */
> -#ifdef __LITTLE_ENDIAN
> -#  define aligned_byte_mask(n) ((1ul << 8*(n))-1)
> -#else
> -#  define aligned_byte_mask(n) (~0xfful << (BITS_PER_LONG - 8 - 8*(n)))
> -#endif
> -
>  /*
>   * Do a strnlen, return length of string *with* final '\0'.
>   * 'count' is the user-supplied count, while 'max' is the
> diff --git a/lib/test_user_copy.c b/lib/test_user_copy.c
> index 67bcd5dfd847..f7cde3845ccc 100644
> --- a/lib/test_user_copy.c
> +++ b/lib/test_user_copy.c
> @@ -31,14 +31,58 @@
>  # define TEST_U64
>  #endif
>  
> -#define test(condition, msg)		\
> -({					\
> -	int cond = (condition);		\
> -	if (cond)			\
> -		pr_warn("%s\n", msg);	\
> -	cond;				\
> +#define test(condition, msg, ...)					\
> +({									\
> +	int cond = (condition);						\
> +	if (cond)							\
> +		pr_warn("[%d] " msg "\n", __LINE__, ##__VA_ARGS__);	\
> +	cond;								\
>  })
>  
> +static int test_is_zeroed_user(char *kmem, char __user *umem, size_t size)
> +{
> +	int ret = 0;
> +	size_t start, end, i;
> +	size_t zero_start = size / 4;
> +	size_t zero_end = size - zero_start;
> +
> +	/*
> +	 * We conduct a series of is_zeroed_user() tests on a block of memory
> +	 * with the following byte-pattern (trying every possible [start,end]
> +	 * pair):
> +	 *
> +	 *   [ 00 ff 00 ff ... 00 00 00 00 ... ff 00 ff 00 ]
> +	 *
> +	 * And we verify that is_zeroed_user() acts identically to memchr_inv().
> +	 */
> +
> +	for (i = 0; i < zero_start; i += 2)
> +		kmem[i] = 0x00;
> +	for (i = 1; i < zero_start; i += 2)
> +		kmem[i] = 0xff;
> +
> +	for (i = zero_end; i < size; i += 2)
> +		kmem[i] = 0xff;
> +	for (i = zero_end + 1; i < size; i += 2)
> +		kmem[i] = 0x00;
> +
> +	ret |= test(copy_to_user(umem, kmem, size),
> +		    "legitimate copy_to_user failed");
> +
> +	for (start = 0; start <= size; start++) {
> +		for (end = start; end <= size; end++) {
> +			int retval = is_zeroed_user(umem + start, end - start);
> +			int expected = memchr_inv(kmem + start, 0, end - start) == NULL;
> +
> +			ret |= test(retval != expected,
> +				    "is_zeroed_user(=%d) != memchr_inv(=%d) mismatch (start=%lu, end=%lu)",
> +				    retval, expected, start, end);
> +		}
> +	}
> +
> +	return ret;
> +}
> +
>  static int __init test_user_copy_init(void)
>  {
>  	int ret = 0;
> @@ -106,6 +150,9 @@ static int __init test_user_copy_init(void)
>  #endif
>  #undef test_legit
>  
> +	/* Test usage of is_zeroed_user(). */
> +	ret |= test_is_zeroed_user(kmem, usermem, PAGE_SIZE);
> +
>  	/*
>  	 * Invalid usage: none of these copies should succeed.
>  	 */
> diff --git a/lib/usercopy.c b/lib/usercopy.c
> index c2bfbcaeb3dc..f795cf0946ad 100644
> --- a/lib/usercopy.c
> +++ b/lib/usercopy.c
> @@ -1,5 +1,6 @@
>  // SPDX-License-Identifier: GPL-2.0
>  #include <linux/uaccess.h>
> +#include <linux/bitops.h>
>  
>  /* out-of-line parts */
>  
> @@ -31,3 +32,117 @@ unsigned long _copy_to_user(void __user *to, const void *from, unsigned long n)
>  }
>  EXPORT_SYMBOL(_copy_to_user);
>  #endif
> +
> +/**
> + * is_zeroed_user: check if a userspace buffer is full of zeros
> + * @from:  Source address, in userspace.
> + * @size: Size of buffer.
> + *
> + * This is effectively shorthand for "memchr_inv(from, 0, size) == NULL" for
> + * userspace addresses. If there are non-zero bytes present then false is
> + * returned, otherwise true is returned.
> + *
> + * Returns:
> + *  * -EFAULT: access to userspace failed.
> + */
> +int is_zeroed_user(const void __user *from, size_t size)

See my bool vs int comment from yesterday and [1] for a suggestion.

> +{
> +	unsigned long val;
> +	uintptr_t align = (uintptr_t) from % sizeof(unsigned long);
> +
> +	if (unlikely(!size))
> +		return true;
> +
> +	from -= align;
> +	size += align;
> +
> +	if (!user_access_begin(from, size))
> +		return -EFAULT;
> +
> +	unsafe_get_user(val, (unsigned long __user *) from, err_fault);
> +	if (align)
> +		val &= ~aligned_byte_mask(align);
> +
> +	while (size > sizeof(unsigned long)) {
> +		if (unlikely(val))
> +			goto done;
> +
> +		from += sizeof(unsigned long);
> +		size -= sizeof(unsigned long);
> +
> +		unsafe_get_user(val, (unsigned long __user *) from, err_fault);
> +	}
> +
> +	if (size < sizeof(unsigned long))
> +		val &= aligned_byte_mask(size);
> +
> +done:
> +	user_access_end();
> +	return (val == 0);
> +err_fault:
> +	user_access_end();
> +	return -EFAULT;
> +}
> +EXPORT_SYMBOL(is_zeroed_user);


> +
> +/**
> + * copy_struct_from_user: copy a struct from userspace
> + * @dst:   Destination address, in kernel space. This buffer must be @ksize
> + *         bytes long.
> + * @ksize: Size of @dst struct.
> + * @src:   Source address, in userspace.
> + * @usize: (Alleged) size of @src struct.
> + *
> + * Copies a struct from userspace to kernel space, in a way that guarantees
> + * backwards-compatibility for struct syscall arguments (as long as future
> + * struct extensions are made such that all new fields are *appended* to the
> + * old struct, and zeroed-out new fields have the same meaning as the old
> + * struct).
> + *
> + * @ksize is just sizeof(*dst), and @usize should've been passed by userspace.
> + * The recommended usage is something like the following:
> + *
> + *   SYSCALL_DEFINE2(foobar, const struct foo __user *, uarg, size_t, usize)
> + *   {
> + *      int err;
> + *      struct foo karg = {};
> + *
> + *      err = copy_struct_from_user(&karg, sizeof(karg), uarg, size);
> + *      if (err)
> + *        return err;
> + *
> + *      // ...
> + *   }
> + *
> + * There are three cases to consider:
> + *  * If @usize == @ksize, then it's copied verbatim.
> + *  * If @usize < @ksize, then the userspace has passed an old struct to a
> + *    newer kernel. The rest of the trailing bytes in @dst (@ksize - @usize)
> + *    are to be zero-filled.
> + *  * If @usize > @ksize, then the userspace has passed a new struct to an
> + *    older kernel. The trailing bytes unknown to the kernel (@usize - @ksize)
> + *    are checked to ensure they are zeroed, otherwise -E2BIG is returned.
> + *
> + * Returns (in all cases, some data may have been copied):
> + *  * -E2BIG:  (@usize > @ksize) and there are non-zero trailing bytes in @src.
> + *  * -EFAULT: access to userspace failed.
> + */
> +int copy_struct_from_user(void *dst, size_t ksize,
> +			  const void __user *src, size_t usize)
> +{
> +	size_t size = min(ksize, usize);
> +	size_t rest = max(ksize, usize) - size;
> +
> +	/* Deal with trailing bytes. */
> +	if (usize < ksize) {
> +		memset(dst + size, 0, rest);
> +	} else if (usize > ksize) {
> +		int ret = is_zeroed_user(src + size, rest);
> +		if (ret <= 0)
> +			return ret ?: -E2BIG;
> +	}
> +	/* Copy the interoperable parts of the struct. */
> +	if (copy_from_user(dst, src, size))
> +		return -EFAULT;
> +	return 0;
> +}
> -- 
> 2.23.0
> 

[1]: How about:

/**
 * <sensible documentation>
 * 
 * Returns 1, if the user buffer is zeroed, 0 if it is not, and a
 * negative error code otherwise.
 * 
 */
int memuser_zero(const void __user *from, size_t size)
{
	unsigned long val;
	uintptr_t align = (uintptr_t) from % sizeof(unsigned long);

	if (unlikely(size == 0))
		return 1;

	from -= align;
	size += align;

	if (!user_access_begin(from, size))
		return -EFAULT;

	unsafe_get_user(val, (unsigned long __user *) from, err_fault);
	if (align)
		val &= ~aligned_byte_mask(align);

	while (size > sizeof(unsigned long)) {
		if (unlikely(val))
			goto err_fault;

		from += sizeof(unsigned long);
		size -= sizeof(unsigned long);

		unsafe_get_user(val, (unsigned long __user *) from, err_fault);
	}

	if (size < sizeof(unsigned long))
		val &= aligned_byte_mask(size);

done:
	user_access_end();
	return (val == 0);
err_fault:
	user_access_end();
	return -EFAULT;
}

int copy_struct_from_user(void *dst, size_t ksize,
			  const void __user *src, size_t usize)
{
	size_t size = min(ksize, usize);
	size_t rest = max(ksize, usize) - size;

	/* Deal with trailing bytes. */
	if (usize < ksize) {
		memset(dst + size, 0, rest);
	} else if ((usize > ksize) {
 		int ret = memuser_zero(src + size, rest);
		if (ret < 0) /* we failed to check the user memory somehow */
			return ret;
		if (ret == 0) /* some of the memory was non-zero */
			return -E2BIG;
	}

	/* Copy the interoperable parts of the struct. */
	if (copy_from_user(dst, src, size))
		return -EFAULT;
	return 0;
}

Re: [PATCH v2 1/4] lib: introduce copy_struct_from_user() helper

[Aleksa Sarai]

[-- Attachment #1: Type: text/plain, Size: 1384 bytes --]

On 2019-09-26, Christian Brauner <christian.brauner@ubuntu.com> wrote:
> On Thu, Sep 26, 2019 at 01:03:29AM +0200, Aleksa Sarai wrote:
> > +int is_zeroed_user(const void __user *from, size_t size)
> > +{
> > +	unsigned long val;
> > +	uintptr_t align = (uintptr_t) from % sizeof(unsigned long);
> > +
> > +	if (unlikely(!size))
> > +		return true;
> 
> You're returning "true" and another implicit boolean with (val == 0)
> down below but -EFAULT in other places. But that function is int
> is_zeroed_user() Would probably be good if you either switch to bool
> is_zeroed_user() as the name suggests or rename the function and have
> it return an int everywhere.

I just checked, and in C11 (and presumably in older specs) it is
guaranteed that "true" and "false" from <stdbool.h> have the values 1
and 0 (respectively) [§7.18]. So this is perfectly well-defined.

Personally, I think it's more readable to have:

  if (unlikely(size == 0))
    return true;
  /* ... */
  return (val == 0);

compared to:

  if (unlikely(size == 0))
    return 1;
  /* ... */
  return val ? 0 : 1;

But I will change the function name (to check_zeroed_user) to make it
clearer that it isn't returning a boolean and that you need to check for
negative returns.

-- 
Aleksa Sarai
Senior Software Engineer (Containers)
SUSE Linux GmbH
<https://www.cyphar.com/>

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 228 bytes --]

Re: [PATCH v2 1/4] lib: introduce copy_struct_from_user() helper

[Christian Brauner]

On Fri, Sep 27, 2019 at 11:07:36AM +1000, Aleksa Sarai wrote:
> On 2019-09-26, Christian Brauner <christian.brauner@ubuntu.com> wrote:
> > On Thu, Sep 26, 2019 at 01:03:29AM +0200, Aleksa Sarai wrote:
> > > +int is_zeroed_user(const void __user *from, size_t size)
> > > +{
> > > +	unsigned long val;
> > > +	uintptr_t align = (uintptr_t) from % sizeof(unsigned long);
> > > +
> > > +	if (unlikely(!size))
> > > +		return true;
> > 
> > You're returning "true" and another implicit boolean with (val == 0)
> > down below but -EFAULT in other places. But that function is int
> > is_zeroed_user() Would probably be good if you either switch to bool
> > is_zeroed_user() as the name suggests or rename the function and have
> > it return an int everywhere.
> 
> I just checked, and in C11 (and presumably in older specs) it is
> guaranteed that "true" and "false" from <stdbool.h> have the values 1
> and 0 (respectively) [§7.18]. So this is perfectly well-defined.
> 
If you declare a function as returning an int, return ints and don't mix
returning ints and "proper" C boolean types. This:

static int foo()
{
	if (bla)
		return true;
	return -1;
}

is just messy.

> 
> Personally, I think it's more readable to have:
> 
>   if (unlikely(size == 0))
>     return true;
>   /* ... */
>   return (val == 0);
> 
> compared to:
> 
>   if (unlikely(size == 0))
>     return 1;
>   /* ... */
>   return val ? 0 : 1;

Just do:

if (unlikely(size == 0))
	return 1;
/* ... */
return (val == 0);

You don't need to change the last return.

Also, as I said in a previous mail: Please wait for rc1 (that's just two
days) to be out so you can base your patchset on that as there are
changes in mainline that cause a merge conflict with your changes.

Thanks!
Christian