On Wed, Apr 12, 2023 at 01:44:00PM +0200, Peter Zijlstra wrote:
> On Tue, Apr 11, 2023 at 05:14:00PM -0700, Josh Poimboeuf wrote:
>
> > Peter, what do you think, should we make track uaccess state across
> > function boundaries?
>
> So IIRC the goal was to explicitly dis-allow that. You want minimal code
> executed with STAC and hence disallow calling stuff.
I guess I was wondering if we could make an exception for calls to
static IPA-optimized functions, so we wouldn't have to scramble to "fix"
compiler optimizations.
But for now, yeah let's just keep it simple.
Jens, can you confirm this works? I added __noclone instead of removing
static.
---8<---
From: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
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 <sfr@xxxxxxxxxxxxxxxx>
https://lkml.kernel.org/lkml/20230327120017.6bb826d7@xxxxxxxxxxxxxxxx
Signed-off-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
---
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 =
--
2.39.2
