Messages in this thread Patch in this message | | | From | Ben Dooks <> | Subject | [PATCH] [V2] x86/asm: add __user on copy_user_handle_tail() pointers | Date | Sat, 30 Mar 2019 11:56:24 +0000 |
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The copy_user_handle_tail() clearly uses both from and to as pointers to user-space memory. This triggers sparse warning on using the calls to get and put to user-space. This can be fixed easily by changing the call to take __user annotated pointer.s
arch/x86/lib/usercopy_64.c:68:21: warning: incorrect type in argument 1 (different address spaces) arch/x86/lib/usercopy_64.c:68:21: expected void const volatile [noderef] <asn:1>*<noident> arch/x86/lib/usercopy_64.c:68:21: got char * arch/x86/lib/usercopy_64.c:70:21: warning: incorrect type in argument 1 (different address spaces) arch/x86/lib/usercopy_64.c:70:21: expected void const volatile [noderef] <asn:1>*<noident> arch/x86/lib/usercopy_64.c:70:21: got char *to
From Linus Torvalds:
On Thu, Mar 28, 2019 at 12:24 AM Borislav Petkov <bp@alien8.de> wrote:
Well, but copy_user_generic() (which ends up calling the copy_user_handle_tail() eventually) casts those __user pointers to (__force void *). Converting them back to __user looks strange to me.
Linus?
Well, it does that because the x86 version of copy_user_generic() can work in either direction, so it works when either the source or destination (or both) are user pointers, but they don't _have_ to be.
So the "userness" of a pointer in that context is a bit ambiguous, and so we've picked the pointers to be just plain "void *".
That said, arguably we should have gone the other way and just made them both "__user" pointers, and do the cast the other way around.
But there's no absolutely right answer here, and nobody should ever use copy_user_generic() directly (ie it is very much meant to be only used as a internal helper for the cases that get the pointer annotations right).
Signed-off-by: Ben Dooks <ben.dooks@codethink.co.uk> --- arch/x86/include/asm/uaccess_64.h | 2 +- arch/x86/lib/usercopy_64.c | 2 +- 2 files changed, 2 insertions(+), 2 deletions(-)
diff --git a/arch/x86/include/asm/uaccess_64.h b/arch/x86/include/asm/uaccess_64.h index a9d637bc301d..cbca2cb28939 100644 --- a/arch/x86/include/asm/uaccess_64.h +++ b/arch/x86/include/asm/uaccess_64.h @@ -208,7 +208,7 @@ __copy_from_user_flushcache(void *dst, const void __user *src, unsigned size) } unsigned long -copy_user_handle_tail(char *to, char *from, unsigned len); +copy_user_handle_tail(char __user *to, char __user *from, unsigned len); unsigned long mcsafe_handle_tail(char *to, char *from, unsigned len); diff --git a/arch/x86/lib/usercopy_64.c b/arch/x86/lib/usercopy_64.c index ee42bb0cbeb3..aa180424e77a 100644 --- a/arch/x86/lib/usercopy_64.c +++ b/arch/x86/lib/usercopy_64.c @@ -60,7 +60,7 @@ EXPORT_SYMBOL(clear_user); * it is not necessary to optimize tail handling. */ __visible unsigned long -copy_user_handle_tail(char *to, char *from, unsigned len) +copy_user_handle_tail(char __user *to, char __user *from, unsigned len) { for (; len; --len, to++) { char c; -- 2.20.1
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