The patch titled
Subject: include/linux/uaccess.h: add probe_user_read()
has been added to the -mm tree. Its filename is
mm-add-probe_user_read.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/mm-add-probe_user_read.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/mm-add-probe_user_read.patch
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------------------------------------------------------
From: Christophe Leroy <christophe.leroy@xxxxxx>
Subject: include/linux/uaccess.h: add probe_user_read()
In powerpc code, there are several places implementing safe access to user
data. This is sometimes implemented using probe_kernel_address() with
additional access_ok() verification, sometimes with get_user() enclosed in
a pagefault_disable()/enable() pair, etc:
show_user_instructions()
bad_stack_expansion()
p9_hmi_special_emu()
fsl_pci_mcheck_exception()
read_user_stack_64()
read_user_stack_32() on PPC64
read_user_stack_32() on PPC32
power_pmu_bhrb_to()
In the same spirit as probe_kernel_read(), this patch adds
probe_user_read().
probe_user_read() does the same as probe_kernel_read() but first checks
that it is really a user address.
The patch defines this function as a static inline so the "size" variable
can be examined for const-ness by the check_object_size() in
__copy_from_user_inatomic()
Link: http://lkml.kernel.org/r/39fb6c5a191025378676492e140dc012915ecaeb.1547652372.git.christophe.leroy@xxxxxx
Signed-off-by: Christophe Leroy <christophe.leroy@xxxxxx>
Reviewed-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>
Cc: Paul Mackerras <paulus@xxxxxxxxx>
Cc: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Cc: Mike Rapoport <rppt@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/uaccess.h | 34 ++++++++++++++++++++++++++++++++++
1 file changed, 34 insertions(+)
--- a/include/linux/uaccess.h~mm-add-probe_user_read
+++ a/include/linux/uaccess.h
@@ -263,6 +263,40 @@ extern long strncpy_from_unsafe(char *ds
#define probe_kernel_address(addr, retval) \
probe_kernel_read(&retval, addr, sizeof(retval))
+/**
+ * probe_user_read(): safely attempt to read from a user location
+ * @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.
+ *
+ * We ensure that the copy_from_user is executed in atomic context so that
+ * do_page_fault() doesn't attempt to take mmap_sem. This makes
+ * probe_user_read() suitable for use within regions where the caller
+ * already holds mmap_sem, or other locks which nest inside mmap_sem.
+ *
+ * Returns: 0 on success, -EFAULT on error.
+ */
+
+#ifndef probe_user_read
+static __always_inline long probe_user_read(void *dst, const void __user *src,
+ size_t size)
+{
+ long ret;
+
+ if (!access_ok(src, size))
+ return -EFAULT;
+
+ pagefault_disable();
+ ret = __copy_from_user_inatomic(dst, src, size);
+ pagefault_enable();
+
+ return ret ? -EFAULT : 0;
+}
+#endif
+
#ifndef user_access_begin
#define user_access_begin(ptr,len) access_ok(ptr, len)
#define user_access_end() do { } while (0)
_
Patches currently in -mm which might be from christophe.leroy@xxxxxx are
mm-add-probe_user_read.patch
powerpc-use-probe_user_read.patch
powerpc-use-memblock-functions-returning-virtual-address.patch
