Messages in this thread | | | Date | Thu, 5 Nov 2015 08:44:44 +0100 | Subject | Re: [PATCH 2/2] arm64: Allow changing of attributes outside of modules | From | Ard Biesheuvel <> |
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On 3 November 2015 at 22:48, Laura Abbott <labbott@fedoraproject.org> wrote: > > Currently, the set_memory_* functions that are implemented for arm64 > are restricted to module addresses only. This was mostly done > because arm64 maps normal zone memory with larger page sizes to > improve TLB performance. This has the side effect though of making it > difficult to adjust attributes at the PAGE_SIZE granularity. There are > an increasing number of use cases related to security where it is > necessary to change the attributes of kernel memory. Add functionality > to the page attribute changing code under a Kconfig to let systems > designers decide if they want to make the trade off of security for TLB > pressure. > > Signed-off-by: Laura Abbott <labbott@fedoraproject.org> > --- > arch/arm64/Kconfig.debug | 11 +++++++ > arch/arm64/mm/mm.h | 3 ++ > arch/arm64/mm/mmu.c | 2 +- > arch/arm64/mm/pageattr.c | 74 ++++++++++++++++++++++++++++++++++++++++++++---- > 4 files changed, 84 insertions(+), 6 deletions(-) > > diff --git a/arch/arm64/Kconfig.debug b/arch/arm64/Kconfig.debug > index d6285ef..abc6922 100644 > --- a/arch/arm64/Kconfig.debug > +++ b/arch/arm64/Kconfig.debug > @@ -89,6 +89,17 @@ config DEBUG_ALIGN_RODATA > > If in doubt, say N > > +config DEBUG_CHANGE_PAGEATTR
I don't think this belongs in Kconfig.debug, and I don't think this should default to off.
We know we currently have no users of set_memory_xx() in arch/arm64 that operate on linear mapping addresses, so we will not introduce any performance regressions by adding this functionality now. By putting this feature behind a debug option, every newly introduced call set_memory_xx() that operates on linear or vmalloc() addresses needs to deal with -EINVAL (or depend on DEBUG_CHANGE_PAGEATTR), or it may error out at runtime if the feature is not enabled.
> + bool "Allow all kernel memory to have attributes changed" > + help > + If this option is selected, APIs that change page attributes > + (RW <-> RO, X <-> NX) will be valid for all memory mapped in > + the kernel space. The trade off is that there may be increased > + TLB pressure from finer grained page mapping. Turn on this option > + if performance is more important than security > +
This is backwards
> + If in doubt, say N > + > source "drivers/hwtracing/coresight/Kconfig" > > endmenu
[...]
> diff --git a/arch/arm64/mm/pageattr.c b/arch/arm64/mm/pageattr.c > index e47ed1c..48a4ce9 100644 > --- a/arch/arm64/mm/pageattr.c > +++ b/arch/arm64/mm/pageattr.c
[...]
> @@ -45,17 +108,18 @@ static int change_memory_common(unsigned long addr, int numpages, > int ret; > struct page_change_data data; > > + if (addr < PAGE_OFFSET && !is_vmalloc_addr((void *)addr)) > + return -EINVAL; > +
Doesn't this exclude the module area?
> if (!IS_ALIGNED(addr, PAGE_SIZE)) { > start &= PAGE_MASK; > end = start + size; > WARN_ON_ONCE(1); > } > > - if (start < MODULES_VADDR || start >= MODULES_END) > - return -EINVAL; > - > - if (end < MODULES_VADDR || end >= MODULES_END) > - return -EINVAL; > + ret = check_address(addr); > + if (ret) > + return ret; > > data.set_mask = set_mask; > data.clear_mask = clear_mask; > -- > 2.4.3 >
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