[PATCH 10/23] maccess: unify the probe kernel arch hooks

Christoph Hellwig
2020-05-21T15:25:27Z

Currently architectures have to override every routine that probes
kernel memory, which includes a pure read and strcpy, both in strict
and not strict variants. Just provide a single arch hooks instead to
make sure all architectures cover all the cases.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
arch/parisc/lib/memcpy.c | 12 ++++------
arch/um/kernel/maccess.c | 10 ++++----
arch/x86/mm/maccess.c | 33 ++++++++++-----------------
include/linux/uaccess.h | 6 +++--
mm/maccess.c | 49 ++++++++++++++++++++++++++++++----------
5 files changed, 61 insertions(+), 49 deletions(-)

diff --git a/arch/parisc/lib/memcpy.c b/arch/parisc/lib/memcpy.c
index beceaab34ecb7..5b75c35d1da0d 100644
--- a/arch/parisc/lib/memcpy.c
+++ b/arch/parisc/lib/memcpy.c
@@ -57,14 +57,10 @@ void * memcpy(void * dst,const void *src, size_t count)
EXPORT_SYMBOL(raw_copy_in_user);
EXPORT_SYMBOL(memcpy);

-long probe_kernel_read(void *dst, const void *src, size_t size)
+bool probe_kernel_read_allowed(const void *unsafe_src, size_t size, bool strict)
{
- unsigned long addr = (unsigned long)src;
-
- if (addr < PAGE_SIZE)
- return -EFAULT;
-
+ if ((unsigned long)unsafe_src < PAGE_SIZE)
+ return false;
/* check for I/O space F_EXTEND(0xfff00000) access as well? */
-
- return __probe_kernel_read(dst, src, size);
+ return true;
}
diff --git a/arch/um/kernel/maccess.c b/arch/um/kernel/maccess.c
index 67b2e0fa92bba..ad2c538ce497c 100644
--- a/arch/um/kernel/maccess.c
+++ b/arch/um/kernel/maccess.c
@@ -7,15 +7,13 @@
#include <linux/kernel.h>
#include <os.h>

-long probe_kernel_read(void *dst, const void *src, size_t size)
+bool probe_kernel_read_allowed(const void *src, size_t size, bool strict)
{
void *psrc = (void *)rounddown((unsigned long)src, PAGE_SIZE);

if ((unsigned long)src < PAGE_SIZE || size <= 0)
- return -EFAULT;
-
+ return false;
if (os_mincore(psrc, size + src - psrc) <= 0)
- return -EFAULT;
-
- return __probe_kernel_read(dst, src, size);
+ return false;
+ return true;
}
diff --git a/arch/x86/mm/maccess.c b/arch/x86/mm/maccess.c
index 62c4017a2473d..a96a56ff16109 100644
--- a/arch/x86/mm/maccess.c
+++ b/arch/x86/mm/maccess.c
@@ -9,35 +9,26 @@ static __always_inline u64 canonical_address(u64 vaddr, u8 vaddr_bits)
return ((s64)vaddr << (64 - vaddr_bits)) >> (64 - vaddr_bits);
}

-static __always_inline bool invalid_probe_range(u64 vaddr)
+bool probe_kernel_read_allowed(const void *unsafe_src, size_t size, bool strict)
{
+ unsigned long vaddr = (unsigned long)unsafe_src;
+
+ if (!strict)
+ return true;
+
/*
* Range covering the highest possible canonical userspace address
* as well as non-canonical address range. For the canonical range
* we also need to include the userspace guard page.
*/
- return vaddr < TASK_SIZE_MAX + PAGE_SIZE ||
- canonical_address(vaddr, boot_cpu_data.x86_virt_bits) != vaddr;
+ return vaddr >= TASK_SIZE_MAX + PAGE_SIZE &&
+ canonical_address(vaddr, boot_cpu_data.x86_virt_bits) == vaddr;
}
#else
-static __always_inline bool invalid_probe_range(u64 vaddr)
+bool probe_kernel_read_allowed(const void *unsafe_src, size_t size, bool strict)
{
- return vaddr < TASK_SIZE_MAX;
+ if (!strict)
+ return true;
+ return (unsigned long)vaddr >= TASK_SIZE_MAX;
}
#endif
-
-long probe_kernel_read_strict(void *dst, const void *src, size_t size)
-{
- if (unlikely(invalid_probe_range((unsigned long)src)))
- return -EFAULT;
-
- return __probe_kernel_read(dst, src, size);
-}
-
-long strncpy_from_kernel_nofault(char *dst, const void *unsafe_addr, long count)
-{
- if (unlikely(invalid_probe_range((unsigned long)unsafe_addr)))
- return -EFAULT;
-
- return __strncpy_from_unsafe(dst, unsafe_addr, count);
-}
diff --git a/include/linux/uaccess.h b/include/linux/uaccess.h
index d8366f8468664..65a37ae3b8871 100644
--- a/include/linux/uaccess.h
+++ b/include/linux/uaccess.h
@@ -301,9 +301,11 @@ copy_struct_from_user(void *dst, size_t ksize, const void __user *src,
return 0;
}

+bool probe_kernel_read_allowed(const void *unsafe_src, size_t size,
+ bool strict);
+
extern long probe_kernel_read(void *dst, const void *src, size_t size);
extern long probe_kernel_read_strict(void *dst, const void *src, size_t size);
-extern long __probe_kernel_read(void *dst, const void *src, size_t size);
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);
@@ -312,7 +314,7 @@ extern long notrace probe_user_write(void __user *dst, const void *src, size_t s
extern long strncpy_from_unsafe(char *dst, const void *unsafe_addr, long count);
long strncpy_from_kernel_nofault(char *dst, const void *unsafe_addr,
long count);
-extern long __strncpy_from_unsafe(char *dst, const void *unsafe_addr, long count);
+
long strncpy_from_user_nofault(char *dst, const void __user *unsafe_addr,
long count);
long strnlen_user_nofault(const void __user *unsafe_addr, long count);
diff --git a/mm/maccess.c b/mm/maccess.c
index 31cf6604e7fff..6116742608217 100644
--- a/mm/maccess.c
+++ b/mm/maccess.c
@@ -6,6 +6,17 @@
#include <linux/mm.h>
#include <linux/uaccess.h>

+static long __probe_kernel_read(void *dst, const void *src, size_t size,
+ bool strict);
+static long __strncpy_from_unsafe(char *dst, const void *unsafe_addr,
+ long count, bool strict);
+
+bool __weak probe_kernel_read_allowed(const void *unsafe_src, size_t size,
+ bool strict)
+{
+ return true;
+}
+
/**
* probe_kernel_read(): safely attempt to read from any location
* @dst: pointer to the buffer that shall take the data
@@ -19,8 +30,11 @@
* DO NOT USE THIS FUNCTION - it is broken on architectures with entirely
* separate kernel and user address spaces, and also a bad idea otherwise.
*/
-long __weak probe_kernel_read(void *dst, const void *src, size_t size)
- __attribute__((alias("__probe_kernel_read")));
+long probe_kernel_read(void *dst, const void *src, size_t size)
+{
+ return __probe_kernel_read(dst, src, size, false);
+}
+EXPORT_SYMBOL_GPL(probe_kernel_read);

/**
* probe_kernel_read_strict(): safely attempt to read from kernel-space
@@ -36,14 +50,20 @@ long __weak probe_kernel_read(void *dst, const void *src, size_t size)
* probe_kernel_read() suitable for use within regions where the caller
* already holds mmap_sem, or other locks which nest inside mmap_sem.
*/
-long __weak probe_kernel_read_strict(void *dst, const void *src, size_t size)
- __attribute__((alias("__probe_kernel_read")));
+long probe_kernel_read_strict(void *dst, const void *src, size_t size)
+{
+ return __probe_kernel_read(dst, src, size, true);
+}

-long __probe_kernel_read(void *dst, const void *src, size_t size)
+static long __probe_kernel_read(void *dst, const void *src, size_t size,
+ bool strict)
{
long ret;
mm_segment_t old_fs = get_fs();

+ if (!probe_kernel_read_allowed(src, size, strict))
+ return -EFAULT;
+
set_fs(KERNEL_DS);
pagefault_disable();
ret = __copy_from_user_inatomic(dst, (__force const void __user *)src,
@@ -55,7 +75,6 @@ long __probe_kernel_read(void *dst, const void *src, size_t size)
return -EFAULT;
return 0;
}
-EXPORT_SYMBOL_GPL(probe_kernel_read);

/**
* probe_user_read(): safely attempt to read from a user-space location
@@ -161,8 +180,10 @@ long probe_user_write(void __user *dst, const void *src, size_t size)
* DO NOT USE THIS FUNCTION - it is broken on architectures with entirely
* separate kernel and user address spaces, and also a bad idea otherwise.
*/
-long __weak strncpy_from_unsafe(char *dst, const void *unsafe_addr, long count)
- __attribute__((alias("__strncpy_from_unsafe")));
+long strncpy_from_unsafe(char *dst, const void *unsafe_addr, long count)
+{
+ return __strncpy_from_unsafe(dst, unsafe_addr, count, false);
+}

/**
* strncpy_from_kernel_nofault: - Copy a NUL terminated string from unsafe
@@ -182,11 +203,13 @@ long __weak strncpy_from_unsafe(char *dst, const void *unsafe_addr, long count)
* 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 __weak strncpy_from_kernel_nofault(char *dst, const void *unsafe_addr,
- long count)
- __attribute__((alias("__strncpy_from_unsafe")));
+long strncpy_from_kernel_nofault(char *dst, const void *unsafe_addr, long count)
+{
+ return __strncpy_from_unsafe(dst, unsafe_addr, count, true);
+}

-long __strncpy_from_unsafe(char *dst, const void *unsafe_addr, long count)
+static long __strncpy_from_unsafe(char *dst, const void *unsafe_addr,
+ long count, bool strict)
{
mm_segment_t old_fs = get_fs();
const void *src = unsafe_addr;
@@ -194,6 +217,8 @@ long __strncpy_from_unsafe(char *dst, const void *unsafe_addr, long count)

if (unlikely(count <= 0))
return 0;
+ if (!probe_kernel_read_allowed(unsafe_addr, count, strict))
+ return -EFAULT;

set_fs(KERNEL_DS);
pagefault_disable();
--
2.26.2