Re: [PATCH v2 1/2] mm: add probe_user_read()
flat view
From: Mike Rapoport <hidden>
Date: 2019-01-08 07:51:15
Also in:
linux-mm, lkml
On Tue, Jan 08, 2019 at 07:37:44AM +0000, Christophe Leroy wrote:
quoted hunk ↗ jump to hunk
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. Signed-off-by: Christophe Leroy <redacted> --- v2: Added "Returns:" comment and removed probe_user_address() Changes since RFC: Made a static inline function instead of weak function as recommended by Kees. include/linux/uaccess.h | 34 ++++++++++++++++++++++++++++++++++ 1 file changed, 34 insertions(+)diff --git a/include/linux/uaccess.h b/include/linux/uaccess.h index 37b226e8df13..07f4f0ed69bc 100644 --- a/include/linux/uaccess.h +++ b/include/linux/uaccess.h@@ -263,6 +263,40 @@ extern long strncpy_from_unsafe(char *dst, const void *unsafe_addr, long count); #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 + * + * Returns: 0 on success, -EFAULT on error.
Nit: please put the "Returns:" comment after the description, otherwise kernel-doc considers it a part of the elaborate description.
+ *
+ * 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.
+ */
+
+#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)
--
2.13.3-- Sincerely yours, Mike.