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SubjectRe: [PATCH] Convert filldir[64]() from __put_user() to unsafe_put_user()
On Mon, Oct 7, 2019 at 11:36 AM Tony Luck <tony.luck@gmail.com> wrote:
>
> Late to this party ,,, but my ia64 console today is full of:

Hmm? I thought ia64 did unaligneds ok.

But regardless, this is my current (as yet untested) patch. This is
not the big user access cleanup that I hope Al will do, this is just a
"ok, x86 is the only one who wants a special unsafe_copy_to_user()
right now" patch.

Linus
arch/x86/include/asm/uaccess.h | 23 ++++++++++++++++++++++
fs/readdir.c | 44 ++----------------------------------------
include/linux/uaccess.h | 6 ++++--
3 files changed, 29 insertions(+), 44 deletions(-)

diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h
index 35c225ede0e4..61d93f062a36 100644
--- a/arch/x86/include/asm/uaccess.h
+++ b/arch/x86/include/asm/uaccess.h
@@ -734,5 +734,28 @@ do { \
if (unlikely(__gu_err)) goto err_label; \
} while (0)

+/*
+ * We want the unsafe accessors to always be inlined and use
+ * the error labels - thus the macro games.
+ */
+#define unsafe_copy_loop(dst, src, len, type, label) \
+ while (len >= sizeof(type)) { \
+ unsafe_put_user(*(type *)src,(type __user *)dst,label); \
+ dst += sizeof(type); \
+ src += sizeof(type); \
+ len -= sizeof(type); \
+ }
+
+#define unsafe_copy_to_user(_dst,_src,_len,label) \
+do { \
+ char __user *__ucu_dst = (_dst); \
+ const char *__ucu_src = (_src); \
+ size_t __ucu_len = (_len); \
+ unsafe_copy_loop(__ucu_dst, __ucu_src, __ucu_len, u64, label); \
+ unsafe_copy_loop(__ucu_dst, __ucu_src, __ucu_len, u32, label); \
+ unsafe_copy_loop(__ucu_dst, __ucu_src, __ucu_len, u16, label); \
+ unsafe_copy_loop(__ucu_dst, __ucu_src, __ucu_len, u8, label); \
+} while (0)
+
#endif /* _ASM_X86_UACCESS_H */

diff --git a/fs/readdir.c b/fs/readdir.c
index 19bea591c3f1..6e2623e57b2e 100644
--- a/fs/readdir.c
+++ b/fs/readdir.c
@@ -27,53 +27,13 @@
/*
* Note the "unsafe_put_user() semantics: we goto a
* label for errors.
- *
- * Also note how we use a "while()" loop here, even though
- * only the biggest size needs to loop. The compiler (well,
- * at least gcc) is smart enough to turn the smaller sizes
- * into just if-statements, and this way we don't need to
- * care whether 'u64' or 'u32' is the biggest size.
- */
-#define unsafe_copy_loop(dst, src, len, type, label) \
- while (len >= sizeof(type)) { \
- unsafe_put_user(get_unaligned((type *)src), \
- (type __user *)dst, label); \
- dst += sizeof(type); \
- src += sizeof(type); \
- len -= sizeof(type); \
- }
-
-/*
- * We avoid doing 64-bit copies on 32-bit architectures. They
- * might be better, but the component names are mostly small,
- * and the 64-bit cases can end up being much more complex and
- * put much more register pressure on the code, so it's likely
- * not worth the pain of unaligned accesses etc.
- *
- * So limit the copies to "unsigned long" size. I did verify
- * that at least the x86-32 case is ok without this limiting,
- * but I worry about random other legacy 32-bit cases that
- * might not do as well.
- */
-#define unsafe_copy_type(dst, src, len, type, label) do { \
- if (sizeof(type) <= sizeof(unsigned long)) \
- unsafe_copy_loop(dst, src, len, type, label); \
-} while (0)
-
-/*
- * Copy the dirent name to user space, and NUL-terminate
- * it. This should not be a function call, since we're doing
- * the copy inside a "user_access_begin/end()" section.
*/
#define unsafe_copy_dirent_name(_dst, _src, _len, label) do { \
char __user *dst = (_dst); \
const char *src = (_src); \
size_t len = (_len); \
- unsafe_copy_type(dst, src, len, u64, label); \
- unsafe_copy_type(dst, src, len, u32, label); \
- unsafe_copy_type(dst, src, len, u16, label); \
- unsafe_copy_type(dst, src, len, u8, label); \
- unsafe_put_user(0, dst, label); \
+ unsafe_put_user(0, dst+len, label); \
+ unsafe_copy_to_user(dst, src, len, label); \
} while (0)


diff --git a/include/linux/uaccess.h b/include/linux/uaccess.h
index e47d0522a1f4..d4ee6e942562 100644
--- a/include/linux/uaccess.h
+++ b/include/linux/uaccess.h
@@ -355,8 +355,10 @@ extern long strnlen_unsafe_user(const void __user *unsafe_addr, long count);
#ifndef user_access_begin
#define user_access_begin(ptr,len) access_ok(ptr, len)
#define user_access_end() do { } while (0)
-#define unsafe_get_user(x, ptr, err) do { if (unlikely(__get_user(x, ptr))) goto err; } while (0)
-#define unsafe_put_user(x, ptr, err) do { if (unlikely(__put_user(x, ptr))) goto err; } while (0)
+#define unsafe_op_wrap(op, err) do { if (unlikely(op)) goto err; } while (0)
+#define unsafe_get_user(x,p,e) unsafe_op_wrap(__get_user(x,p),e)
+#define unsafe_put_user(x,p,e) unsafe_op_wrap(__put_user(x,p),e)
+#define unsafe_copy_to_user(d,s,l,e) unsafe_op_wrap(__copy_to_user(d,s,l),e)
static inline unsigned long user_access_save(void) { return 0UL; }
static inline void user_access_restore(unsigned long flags) { }
#endif
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