Re: [PATCH 1/2] mm: add probe_user_read() and probe_user_address()
From: Mike Rapoport <hidden>
Date: 2018-12-03 17:54:09
Also in:
linux-mm, lkml
On Mon, Dec 03, 2018 at 05:06:42PM +0000, Christophe Leroy wrote:
quoted hunk ↗ jump to hunk
In the powerpc, 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() and probe_kernel_address(), this patch adds probe_user_read() and probe_user_address(). probe_user_read() does the same as probe_kernel_read() but first checks that it is really a user address. probe_user_address() is a shortcut to probe_user_read() Signed-off-by: Christophe Leroy <redacted> --- Changes since RFC: Made a static inline function instead of weak function as recommended by Kees. include/linux/uaccess.h | 42 ++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 42 insertions(+)diff --git a/include/linux/uaccess.h b/include/linux/uaccess.h index efe79c1cdd47..83ea8aefca75 100644 --- a/include/linux/uaccess.h +++ b/include/linux/uaccess.h@@ -266,6 +266,48 @@ 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 + * + * 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.
Please add 'Returns:' description.
+ */
+
+#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(VERIFY_READ, src, size))
+ return -EFAULT;
+
+ pagefault_disable();
+ ret = __copy_from_user_inatomic(dst, src, size);
+ pagefault_enable();
+
+ return ret ? -EFAULT : 0;
+}
+#endif
+
+/**
+ * probe_user_address(): safely attempt to read from a user location
+ * @addr: address to read from
+ * @retval: read into this variable
+ *
+ * Returns 0 on success, or -EFAULT.This should be 'Return:' for kernel-doc to recognise it as return value description.
+ */
+#define probe_user_address(addr, retval) \
+ probe_user_read(&(retval), addr, sizeof(retval))
+
#ifndef user_access_begin
#define user_access_begin() do { } while (0)
#define user_access_end() do { } while (0)
--
2.13.3-- Sincerely yours, Mike.