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...

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/CAOUHufaPshtKrTWOz7T7QFYUNVGFm0JBjvM700Nhf9qEL9b... 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