+ x86-uaccess-avoid-check_object_size-in-copy_from_user_nmi.patch added to mm-hotfixes-unstable branch

+ x86-uaccess-avoid-check_object_size-in-copy_from_user_nmi.patch added to mm-hotfixes-unstable branch

[Andrew Morton]

The patch titled
     Subject: x86/uaccess: avoid check_object_size() in copy_from_user_nmi()
has been added to the -mm mm-hotfixes-unstable branch.  Its filename is
     x86-uaccess-avoid-check_object_size-in-copy_from_user_nmi.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/x86-uaccess-avoid-check_object_size-in-copy_from_user_nmi.patch

This patch will later appear in the mm-hotfixes-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Kees Cook <keescook@chromium.org>
Subject: x86/uaccess: avoid check_object_size() in copy_from_user_nmi()
Date: Mon, 19 Sep 2022 13:16:48 -0700

The check_object_size() helper under CONFIG_HARDENED_USERCOPY is designed
to skip any checks where the length is known at compile time as a
reasonable heuristic to avoid "likely known-good" cases.  However, it can
only do this when the copy_*_user() helpers are, themselves, inline too.

Using find_vmap_area() requires taking a spinlock.  The
check_object_size() helper can call find_vmap_area() when the destination
is in vmap memory.  If show_regs() is called in interrupt context, it will
attempt a call to copy_from_user_nmi(), which may call check_object_size()
and then find_vmap_area().  If something in normal context happens to be
in the middle of calling find_vmap_area() (with the spinlock held), the
interrupt handler will hang forever.

The copy_from_user_nmi() call is actually being called with a fixed-size
length, so check_object_size() should never have been called in the first
place.  Given the narrow constraints, just replace the
__copy_from_user_inatomic() call with an open-coded version that calls
only into the sanitizers and not check_object_size(), followed by a call
to raw_copy_from_user().

Link: https://lkml.kernel.org/r/20220919201648.2250764-1-keescook@chromium.org
Link: https://lore.kernel.org/all/CAOUHufaPshtKrTWOz7T7QFYUNVGFm0JBjvM700Nhf9qEL9b3EQ@mail.gmail.com
Fixes: 0aef499f3172 ("mm/usercopy: Detect vmalloc overruns")
Signed-off-by: Kees Cook <keescook@chromium.org>
Reported-by: Yu Zhao <yuzhao@google.com>
Reported-by: <dev@der-flo.net>
Suggested-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Josh Poimboeuf <jpoimboe@kernel.org>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---


--- a/arch/x86/lib/usercopy.c~x86-uaccess-avoid-check_object_size-in-copy_from_user_nmi
+++ a/arch/x86/lib/usercopy.c
@@ -44,7 +44,8 @@ copy_from_user_nmi(void *to, const void
 	 * called from other contexts.
 	 */
 	pagefault_disable();
-	ret = __copy_from_user_inatomic(to, from, n);
+	instrument_copy_from_user(to, from, n);
+	ret = raw_copy_from_user(to, from, n);
 	pagefault_enable();
 
 	return ret;
_

Patches currently in -mm which might be from keescook@chromium.org are

x86-uaccess-avoid-check_object_size-in-copy_from_user_nmi.patch