On Fri, Sep 23, 2022 at 03:17:30PM -0700, Dave Hansen wrote: > The 32-bit code is in a weird spot. Some 32-bit builds (non-PAE) do not > even have NX support. Even PAE builds that support NX have to contend > with things like EFI data and code mixed in the same pages where W+X > is unavoidable. > > The folks still running X86_32=y kernels are unlikely to care much about > NX. That combined with the fundamental inability fix _all_ of the W+X > things means this code had little value on X86_32=y. Disable the checks. > > Reported-by: Guenter Roeck <linux@xxxxxxxxxxxx> > Signed-off-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx> > Cc: Ard Biesheuvel <ardb@xxxxxxxxxx> > Cc: Darren Hart <dvhart@xxxxxxxxxxxxx> > Cc: Andy Shevchenko <andy@xxxxxxxxxxxxx> > Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx> > Cc: Ingo Molnar <mingo@xxxxxxxxxx> > Cc: Borislav Petkov <bp@xxxxxxxxx> > Cc: x86@xxxxxxxxxx > Cc: linux-efi@xxxxxxxxxxxxxxx > Cc: "H. Peter Anvin" <hpa@xxxxxxxxx> > Cc: Kees Cook <keescook@xxxxxxxxxxxx> > Link: https://lore.kernel.org/all/CAMj1kXHcF_iK_g0OZSkSv56Wmr=eQGQwNstcNjLEfS=mm7a06w@xxxxxxxxxxxxxx/ Tested-by: Guenter Roeck <linux@xxxxxxxxxxxx> Guenter > --- > arch/x86/mm/pat/set_memory.c | 8 ++++++++ > 1 file changed, 8 insertions(+) > > diff --git a/arch/x86/mm/pat/set_memory.c b/arch/x86/mm/pat/set_memory.c > index 20b1e24baa85..efe882c753ca 100644 > --- a/arch/x86/mm/pat/set_memory.c > +++ b/arch/x86/mm/pat/set_memory.c > @@ -587,6 +587,14 @@ static inline pgprot_t verify_rwx(pgprot_t old, pgprot_t new, unsigned long star > { > unsigned long end; > > + /* > + * 32-bit has some unfixable W+X issues, like EFI code > + * and writeable data being in the same page. Disable > + * detection and enforcement there. > + */ > + if (IS_ENABLED(CONFIG_X86_32)) > + return new; > + > /* Only enforce when NX is supported: */ > if (!(__supported_pte_mask & _PAGE_NX)) > return new; > -- > 2.34.1 >
