From 384a746bb55960aa5ffb3a67de08f11fc2f51042 Mon Sep 17 00:00:00 2001 From: David Hildenbrand Date: Wed, 5 Jun 2024 11:17:10 +0200 Subject: Revert "mm: init_mlocked_on_free_v3" There was insufficient review and no agreement that this is the right approach. There are serious flaws with the implementation that make processes using mlock() not even work with simple fork() [1] and we get reliable crashes when rebooting. Further, simply because we might be unmapping a single PTE of a large mlocked folio, we shouldn't zero out the whole folio. ... especially because the code can also *corrupt* urelated memory because kernel_init_pages(page, folio_nr_pages(folio)); Could end up writing outside of the actual folio if we work with a tail page. Let's revert it. Once there is agreement that this is the right approach, the issues were fixed and there was reasonable review and proper testing, we can consider it again. [1] https://lkml.kernel.org/r/4da9da2f-73e4-45fd-b62f-a8a513314057@redhat.com Link: https://lkml.kernel.org/r/20240605091710.38961-1-david@redhat.com Fixes: ba42b524a040 ("mm: init_mlocked_on_free_v3") Signed-off-by: David Hildenbrand Reported-by: David Wang <00107082@163.com> Closes: https://lore.kernel.org/lkml/20240528151340.4282-1-00107082@163.com/ Reported-by: Lance Yang Closes: https://lkml.kernel.org/r/20240601140917.43562-1-ioworker0@gmail.com Acked-by: Lance Yang Cc: York Jasper Niebuhr Cc: Matthew Wilcox (Oracle) Cc: Kees Cook Signed-off-by: Andrew Morton --- security/Kconfig.hardening | 15 --------------- 1 file changed, 15 deletions(-) (limited to 'security') diff --git a/security/Kconfig.hardening b/security/Kconfig.hardening index effbf5982be1..2cff851ebfd7 100644 --- a/security/Kconfig.hardening +++ b/security/Kconfig.hardening @@ -255,21 +255,6 @@ config INIT_ON_FREE_DEFAULT_ON touching "cold" memory areas. Most cases see 3-5% impact. Some synthetic workloads have measured as high as 8%. -config INIT_MLOCKED_ON_FREE_DEFAULT_ON - bool "Enable mlocked memory zeroing on free" - depends on !KMSAN - help - This config has the effect of setting "init_mlocked_on_free=1" - on the kernel command line. If it is enabled, all mlocked process - memory is zeroed when freed. This restriction to mlocked memory - improves performance over "init_on_free" but can still be used to - protect confidential data like key material from content exposures - to other processes, as well as live forensics and cold boot attacks. - Any non-mlocked memory is not cleared before it is reassigned. This - configuration can be overwritten by setting "init_mlocked_on_free=0" - on the command line. The "init_on_free" boot option takes - precedence over "init_mlocked_on_free". - config CC_HAS_ZERO_CALL_USED_REGS def_bool $(cc-option,-fzero-call-used-regs=used-gpr) # https://github.com/ClangBuiltLinux/linux/issues/1766 -- cgit v1.2.3