Re: [PATCH 14/14] powerpc: remove address space overrides using set_fs()

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Le 03/09/2020 à 17:56, Christoph Hellwig a écrit :
On Thu, Sep 03, 2020 at 05:49:09PM +0200, Christoph Hellwig wrote:
On Thu, Sep 03, 2020 at 05:43:25PM +0200, Christophe Leroy wrote:


Le 03/09/2020 à 16:22, Christoph Hellwig a écrit :
Stop providing the possibility to override the address space using
set_fs() now that there is no need for that any more.

Signed-off-by: Christoph Hellwig <hch@xxxxxx>
---


   -static inline int __access_ok(unsigned long addr, unsigned long size,
-			mm_segment_t seg)
+static inline bool __access_ok(unsigned long addr, unsigned long size)
   {
-	if (addr > seg.seg)
-		return 0;
-	return (size == 0 || size - 1 <= seg.seg - addr);
+	if (addr >= TASK_SIZE_MAX)
+		return false;
+	return size == 0 || size <= TASK_SIZE_MAX - addr;
   }

You don't need to test size == 0 anymore. It used to be necessary because
of the 'size - 1', as size is unsigned.

Now you can directly do

	return size <= TASK_SIZE_MAX - addr;

If size is 0, this will always be true (because you already know that addr
is not >= TASK_SIZE_MAX

True.  What do you think of Linus' comment about always using the
ppc32 version on ppc64 as well with this?

I have nothing against it. That's only adding a substract, all args are already in registers so that will be in the noise for a modern CPU.


i.e. something like this folded in:

diff --git a/arch/powerpc/include/asm/uaccess.h b/arch/powerpc/include/asm/uaccess.h
index 5363f7fc6dd06c..be070254e50943 100644
--- a/arch/powerpc/include/asm/uaccess.h
+++ b/arch/powerpc/include/asm/uaccess.h
@@ -11,26 +11,14 @@
  #ifdef __powerpc64__
  /* We use TASK_SIZE_USER64 as TASK_SIZE is not constant */
  #define TASK_SIZE_MAX		TASK_SIZE_USER64
-
-/*
- * This check is sufficient because there is a large enough gap between user
- * addresses and the kernel addresses.
- */
-static inline bool __access_ok(unsigned long addr, unsigned long size)
-{
-	return addr < TASK_SIZE_MAX && size < TASK_SIZE_MAX;
-}
-
  #else
  #define TASK_SIZE_MAX		TASK_SIZE
+#endif
static inline bool __access_ok(unsigned long addr, unsigned long size)
  {
-	if (addr >= TASK_SIZE_MAX)
-		return false;
-	return size == 0 || size <= TASK_SIZE_MAX - addr;
+	return addr < TASK_SIZE_MAX && size <= TASK_SIZE_MAX - addr;
  }
-#endif /* __powerpc64__ */
#define access_ok(addr, size) \
  	(__chk_user_ptr(addr),		\



Christophe



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