On Wed, Jan 22, 2025 at 04:57:37PM -0800, Kees Cook wrote: > On Wed, Jan 22, 2025 at 05:19:23PM +0000, Mel Gorman wrote: > > HARDENED_USERCOPY defaults to on if enabled at compile time. Allow > > hardened_usercopy= default to be set at compile time similar to > > init_on_alloc= and init_on_free=. The intent is that hardening > > options that can be disabled at runtime can set their default at > > build time. > > > > Signed-off-by: Mel Gorman <[email protected]> > > --- > > Documentation/admin-guide/kernel-parameters.txt | 4 +++- > > mm/usercopy.c | 3 ++- > > security/Kconfig.hardening | 8 ++++++++ > > 3 files changed, 13 insertions(+), 2 deletions(-) > > > > diff --git a/Documentation/admin-guide/kernel-parameters.txt > > b/Documentation/admin-guide/kernel-parameters.txt > > index 3872bc6ec49d..5d759b20540a 100644 > > --- a/Documentation/admin-guide/kernel-parameters.txt > > +++ b/Documentation/admin-guide/kernel-parameters.txt > > @@ -1773,7 +1773,9 @@ > > allocation boundaries as a proactive defense > > against bounds-checking flaws in the kernel's > > copy_to_user()/copy_from_user() interface. > > - on Perform hardened usercopy checks (default). > > + The default is determined by > > + CONFIG_HARDENED_USERCOPY_DEFAULT_ON. > > + on Perform hardened usercopy checks. > > off Disable hardened usercopy checks. > > > > hardlockup_all_cpu_backtrace= > > diff --git a/mm/usercopy.c b/mm/usercopy.c > > index 83c164aba6e0..4cf33305347a 100644 > > --- a/mm/usercopy.c > > +++ b/mm/usercopy.c > > @@ -255,7 +255,8 @@ void __check_object_size(const void *ptr, unsigned long > > n, bool to_user) > > } > > EXPORT_SYMBOL(__check_object_size); > > > > -static bool enable_checks __initdata = true; > > +static bool enable_checks __initdata = > > + IS_ENABLED(CONFIG_HARDENED_USERCOPY_DEFAULT_ON); > > > > static int __init parse_hardened_usercopy(char *str) > > { > > diff --git a/security/Kconfig.hardening b/security/Kconfig.hardening > > index 9088d613d519..adcc260839c7 100644 > > --- a/security/Kconfig.hardening > > +++ b/security/Kconfig.hardening > > @@ -293,6 +293,14 @@ config HARDENED_USERCOPY > > or are part of the kernel text. This prevents entire classes > > of heap overflow exploits and similar kernel memory exposures. > > > > +config HARDENED_USERCOPY_DEFAULT_ON > > + bool "Harden memory copies by default" > > + depends on HARDENED_USERCOPY > > + default n > > This must be "default HARDENED_USERCOPY" or existing distro builds will > break. All major distros enable this by default, and I don't want to > risk HARDENED_USERCOPY_DEFAULT_ON getting missed and getting globally > disabled. >
Ok. I dislike that HARDENED_USERCOPY will be inconsistent with INIT_ON* but it's not a hill I'm willing to die on. Will be in v3 -- Mel Gorman SUSE Labs
