Subject: Re: linux-next: build warnings after merge of the block tree

From: Peter Zijlstra <[email-masked]>
Date: Fri, 16 Jun 2023 14:43:54 +0200

On Wed, Apr 12, 2023 at 09:25:17AM -0700, Josh Poimboeuf wrote:

> From: Josh Poimboeuf <[email-masked]>
> Subject: [PATCH] iov_iter: Mark copy_compat_iovec_from_user() noinline
> 
> After commit 6376ce56feb6 ("iov_iter: import single vector iovecs as
> ITER_UBUF"), GCC does an inter-procedural compiler optimization which
> moves the user_access_begin() out of copy_compat_iovec_from_user() and
> into its callers:
> 
>   lib/iov_iter.o: warning: objtool: .altinstr_replacement+0x0: redundant UACCESS disable
>   lib/iov_iter.o: warning: objtool: iovec_from_user.part.0+0xc7: call to copy_compat_iovec_from_user.part.0() with UACCESS enabled
>   lib/iov_iter.o: warning: objtool: __import_iovec+0x21d: call to copy_compat_iovec_from_user.part.0() with UACCESS enabled
> 
> Enforce the "no UACCESS enable across function boundaries" rule by
> disabling cloning for copy_compat_iovec_from_user().
> 
> Fixes: 6376ce56feb6 ("iov_iter: import single vector iovecs as ITER_UBUF")
> Reported-by: Stephen Rothwell <[email-masked]>
> https://lkml.kernel.org/lkml/[email-masked]
> Signed-off-by: Josh Poimboeuf <[email-masked]>
> ---
>  lib/iov_iter.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/lib/iov_iter.c b/lib/iov_iter.c
> index 274014e4eafe..48aa9fd99267 100644
> --- a/lib/iov_iter.c
> +++ b/lib/iov_iter.c
> @@ -1698,7 +1698,7 @@ const void *dup_iter(struct iov_iter *new, struct iov_iter *old, gfp_t flags)
>  }
>  EXPORT_SYMBOL(dup_iter);
>  
> -static int copy_compat_iovec_from_user(struct iovec *iov,
> +static __noclone int copy_compat_iovec_from_user(struct iovec *iov,
>  		const struct iovec __user *uvec, unsigned long nr_segs)
>  {
>  	const struct compat_iovec __user *uiov =

I've been getting reports from some anonymous people still using ancient
GCCs (10.4) that also need the following:

---
Subject: iov_iter: Mark copy_iovec_from_user() noclone

Extend commit 50f9a76ef127 ("iov_iter: Mark
copy_compat_iovec_from_user() noinline") to also cover
copy_iovec_from_user(). Different compiler versions cause the same
problem on different functions.

lib/iov_iter.o: warning: objtool: .altinstr_replacement+0x1f: redundant UACCESS disable
lib/iov_iter.o: warning: objtool: iovec_from_user+0x84: call to copy_iovec_from_user.part.0() with UACCESS enabled
lib/iov_iter.o: warning: objtool: __import_iovec+0x143: call to copy_iovec_from_user.part.0() with UACCESS enabled

Fixes: 50f9a76ef127 ("iov_iter: Mark copy_compat_iovec_from_user() noinline")
Signed-off-by: Peter Zijlstra (Intel) <[email-masked]>
---
diff --git a/lib/iov_iter.c b/lib/iov_iter.c
index 960223ed9199..061cc3ed58f5 100644
--- a/lib/iov_iter.c
+++ b/lib/iov_iter.c
@@ -1795,7 +1795,7 @@ static __noclone int copy_compat_iovec_from_user(struct iovec *iov,
 	return ret;
 }
 
-static int copy_iovec_from_user(struct iovec *iov,
+static __noclone int copy_iovec_from_user(struct iovec *iov,
 		const struct iovec __user *uiov, unsigned long nr_segs)
 {
 	int ret = -EFAULT;