| Message ID | 20220923221730.1860518-1-dave.hansen@linux.intel.com |
|---|---|
| State | Accepted |
| Commit | 8c4934f4754057e3577bb1536c6ecc0efa2c966e |
| Headers | show |
| Series | x86/mm: Disable W^X detection and enforcement on 32-bit | expand |
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. Maybe downgrade the check to a warning for X86_32=y?
On 9/23/22 17:12, Dave Hansen wrote: > On 9/23/22 17:09, Kirill A. Shutemov wrote: >> 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. >> Maybe downgrade the check to a warning for X86_32=y? > > But for this EFI case, we really don't want the warning. It's unfixable. > > I'm also not sure we want to go to the trouble to properly silence the > warning in these unfixable cases. There was an argument elsewhere in > the thread that we really shouldn't be warning on things that we don't > have full intentions to fix. I buy that argument. Yes, there are already way too many such useless warnings around. Please don't add more of them. Guenter
On Sat, 24 Sept 2022 at 00:17, Dave Hansen <dave.hansen@linux.intel.com> 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@roeck-us.net> > Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com> > Cc: Ard Biesheuvel <ardb@kernel.org> > Cc: Darren Hart <dvhart@infradead.org> > Cc: Andy Shevchenko <andy@infradead.org> > Cc: Thomas Gleixner <tglx@linutronix.de> > Cc: Ingo Molnar <mingo@redhat.com> > Cc: Borislav Petkov <bp@alien8.de> > Cc: x86@kernel.org > Cc: linux-efi@vger.kernel.org > Cc: "H. Peter Anvin" <hpa@zytor.com> > Cc: Kees Cook <keescook@chromium.org> > Link: https://lore.kernel.org/all/CAMj1kXHcF_iK_g0OZSkSv56Wmr=eQGQwNstcNjLEfS=mm7a06w@mail.gmail.com/ Acked-by: Ard Biesheuvel <ardb@kernel.org> > --- > 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 >
Hi! > 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. > --- > 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; > + You are going from extreme to extreme. W^X is useful on x86-32 at least in some configs, so it would make sense to detect and inform about the issues (perhaps with something like KERN_INFO). Best regards, Pavel
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;
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@roeck-us.net> Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com> Cc: Ard Biesheuvel <ardb@kernel.org> Cc: Darren Hart <dvhart@infradead.org> Cc: Andy Shevchenko <andy@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Ingo Molnar <mingo@redhat.com> Cc: Borislav Petkov <bp@alien8.de> Cc: x86@kernel.org Cc: linux-efi@vger.kernel.org Cc: "H. Peter Anvin" <hpa@zytor.com> Cc: Kees Cook <keescook@chromium.org> Link: https://lore.kernel.org/all/CAMj1kXHcF_iK_g0OZSkSv56Wmr=eQGQwNstcNjLEfS=mm7a06w@mail.gmail.com/ --- arch/x86/mm/pat/set_memory.c | 8 ++++++++ 1 file changed, 8 insertions(+)