x86, powerpc: Rename memcpy_mcsafe() to copy_mc_to_{user, kernel}()

commit ec6347bb43395cb92126788a1a5b25302543f815 upstream.

In reaction to a proposal to introduce a memcpy_mcsafe_fast()
implementation Linus points out that memcpy_mcsafe() is poorly named
relative to communicating the scope of the interface. Specifically what
addresses are valid to pass as source, destination, and what faults /
exceptions are handled.

Of particular concern is that even though x86 might be able to handle
the semantics of copy_mc_to_user() with its common copy_user_generic()
implementation other archs likely need / want an explicit path for this
case:

  On Fri, May 1, 2020 at 11:28 AM Linus Torvalds <torvalds@linux-foundation.org> wrote:
  >
  > On Thu, Apr 30, 2020 at 6:21 PM Dan Williams <dan.j.williams@intel.com> wrote:
  > >
  > > However now I see that copy_user_generic() works for the wrong reason.
  > > It works because the exception on the source address due to poison
  > > looks no different than a write fault on the user address to the
  > > caller, it's still just a short copy. So it makes copy_to_user() work
  > > for the wrong reason relative to the name.
  >
  > Right.
  >
  > And it won't work that way on other architectures. On x86, we have a
  > generic function that can take faults on either side, and we use it
  > for both cases (and for the "in_user" case too), but that's an
  > artifact of the architecture oddity.
  >
  > In fact, it's probably wrong even on x86 - because it can hide bugs -
  > but writing those things is painful enough that everybody prefers
  > having just one function.

Replace a single top-level memcpy_mcsafe() with either
copy_mc_to_user(), or copy_mc_to_kernel().

Introduce an x86 copy_mc_fragile() name as the rename for the
low-level x86 implementation formerly named memcpy_mcsafe(). It is used
as the slow / careful backend that is supplanted by a fast
copy_mc_generic() in a follow-on patch.

One side-effect of this reorganization is that separating copy_mc_64.S
to its own file means that perf no longer needs to track dependencies
for its memcpy_64.S benchmarks.

 [ bp: Massage a bit. ]

Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Tony Luck <tony.luck@intel.com>
Acked-by: Michael Ellerman <mpe@ellerman.id.au>
Cc: <stable@vger.kernel.org>
Link: http://lore.kernel.org/r/CAHk-=wjSqtXAqfUJxFtWNwmguFASTgB0dz1dT3V-78Quiezqbg@mail.gmail.com
Link: https://lkml.kernel.org/r/160195561680.2163339.11574962055305783722.stgit@dwillia2-desk3.amr.corp.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

3 files changed, 19 insertions, 13 deletions

diff --git a/include/linux/string.h b/include/linux/string.h
index 9b7a0632e87a..b1f3894a0a3e 100644
--- a/include/linux/string.h
+++ b/include/linux/string.h
@@ -161,20 +161,13 @@ extern int bcmp(const void *,const void *,__kernel_size_t);
 #ifndef __HAVE_ARCH_MEMCHR
 extern void * memchr(const void *,int,__kernel_size_t);
 #endif
-#ifndef __HAVE_ARCH_MEMCPY_MCSAFE
-static inline __must_check unsigned long memcpy_mcsafe(void *dst,
-		const void *src, size_t cnt)
-{
-	memcpy(dst, src, cnt);
-	return 0;
-}
-#endif
 #ifndef __HAVE_ARCH_MEMCPY_FLUSHCACHE
 static inline void memcpy_flushcache(void *dst, const void *src, size_t cnt)
 {
 	memcpy(dst, src, cnt);
 }
 #endif
+
 void *memchr_inv(const void *s, int c, size_t n);
 char *strreplace(char *s, char old, char new);
 
diff --git a/include/linux/uaccess.h b/include/linux/uaccess.h
index 94b285411659..1ae36bc8db35 100644
--- a/include/linux/uaccess.h
+++ b/include/linux/uaccess.h
@@ -179,6 +179,19 @@ copy_in_user(void __user *to, const void __user *from, unsigned long n)
 }
 #endif
 
+#ifndef copy_mc_to_kernel
+/*
+ * Without arch opt-in this generic copy_mc_to_kernel() will not handle
+ * #MC (or arch equivalent) during source read.
+ */
+static inline unsigned long __must_check
+copy_mc_to_kernel(void *dst, const void *src, size_t cnt)
+{
+	memcpy(dst, src, cnt);
+	return 0;
+}
+#endif
+
 static __always_inline void pagefault_disabled_inc(void)
 {
 	current->pagefault_disabled++;
diff --git a/include/linux/uio.h b/include/linux/uio.h
index 3835a8a8e9ea..f14410c678bd 100644
--- a/include/linux/uio.h
+++ b/include/linux/uio.h
@@ -185,10 +185,10 @@ size_t _copy_from_iter_flushcache(void *addr, size_t bytes, struct iov_iter *i);
 #define _copy_from_iter_flushcache _copy_from_iter_nocache
 #endif
 
-#ifdef CONFIG_ARCH_HAS_UACCESS_MCSAFE
-size_t _copy_to_iter_mcsafe(const void *addr, size_t bytes, struct iov_iter *i);
+#ifdef CONFIG_ARCH_HAS_COPY_MC
+size_t _copy_mc_to_iter(const void *addr, size_t bytes, struct iov_iter *i);
 #else
-#define _copy_to_iter_mcsafe _copy_to_iter
+#define _copy_mc_to_iter _copy_to_iter
 #endif
 
 static __always_inline __must_check
@@ -201,12 +201,12 @@ size_t copy_from_iter_flushcache(void *addr, size_t bytes, struct iov_iter *i)
 }
 
 static __always_inline __must_check
-size_t copy_to_iter_mcsafe(void *addr, size_t bytes, struct iov_iter *i)
+size_t copy_mc_to_iter(void *addr, size_t bytes, struct iov_iter *i)
 {
 	if (unlikely(!check_copy_size(addr, bytes, true)))
 		return 0;
 	else
-		return _copy_to_iter_mcsafe(addr, bytes, i);
+		return _copy_mc_to_iter(addr, bytes, i);
 }
 
 size_t iov_iter_zero(size_t bytes, struct iov_iter *);