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Date: Thu, 5 Nov 2015 17:35:07 -0800 From: Laura Abbott <labbott@...hat.com> To: Ard Biesheuvel <ard.biesheuvel@...aro.org>, Laura Abbott <labbott@...oraproject.org> Cc: Catalin Marinas <catalin.marinas@....com>, Will Deacon <will.deacon@....com>, "linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, Kees Cook <keescook@...omium.org>, Xishi Qiu <qiuxishi@...wei.com>, Mark Rutland <mark.rutland@....com> Subject: Re: [PATCH 2/2] arm64: Allow changing of attributes outside of modules On 11/04/2015 11:44 PM, Ard Biesheuvel wrote: > On 3 November 2015 at 22:48, Laura Abbott <labbott@...oraproject.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@...oraproject.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. > I stuck it in Kconfig.debug to have it match with the rest of the module and DEBUG_RODATA options. I'll pull it out. >> + 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 >> -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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