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Message-ID: <CAGXu5jKW-Kq7BapCs=fbPqMrkof-69bVV6-6DtQAmGk_odC=kQ@mail.gmail.com> Date: Tue, 5 Jan 2016 12:08:22 -0800 From: Kees Cook <keescook@...omium.org> To: Ard Biesheuvel <ard.biesheuvel@...aro.org> Cc: "linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>, "kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>, Will Deacon <will.deacon@....com>, Catalin Marinas <catalin.marinas@....com>, Mark Rutland <mark.rutland@....com>, Leif Lindholm <leif.lindholm@...aro.org>, LKML <linux-kernel@...r.kernel.org>, stuart.yoder@...escale.com, bhupesh.sharma@...escale.com, Arnd Bergmann <arnd@...db.de>, Marc Zyngier <marc.zyngier@....com>, Christoffer Dall <christoffer.dall@...aro.org> Subject: Re: [PATCH v2 00/13] arm64: implement support for KASLR On Wed, Dec 30, 2015 at 7:25 AM, Ard Biesheuvel <ard.biesheuvel@...aro.org> wrote: > This series implements KASLR for arm64, by building the kernel as a PIE > executable that can relocate itself at runtime, and moving it to a random > offset in the vmalloc area. This v2 also implements physical randomization, > i.e., it allows the kernel to deal with being loaded at any physical offset > (modulo the required alignment), and invokes the EFI_RNG_PROTOCOL from the > UEFI stub to obtain random bits and perform the actual randomization of the > physical load address. This is great! Thanks for working through all these details. > Changes since v1/RFC: > - This series now implements fully independent virtual and physical address > randomization at load time. I have recycled some patches from this series: > http://thread.gmane.org/gmane.linux.ports.arm.kernel/455151, and updated the > final UEFI stub patch to randomize the physical address as well. I'd love to get virt/phy separated on x86. There was a series, but it still needs more work. Any one on the kernel-hardening list want to take a stab at this? > - Added a patch to deal with the way KVM on arm64 makes assumptions about the > relation between kernel symbols and the linear mapping (on which the HYP > mapping is based), as these assumptions cease to be valid once we move the > kernel Image out of the linear mapping. > - Updated the module PLT patch so it works on BE kernels as well. > - Moved the constant Image header values to head.S, and updated the linker > script to provide the kernel size using R_AARCH64_ABS32 relocation rather > than a R_AARCH64_ABS64 relocation, since those are always resolved at build > time. This allows me to get rid of the post-build perl script to swab header > values on BE kernels. > - Minor style tweaks. > > Notes: > - These patches apply on top of Mark Rutland's pagetable rework series: > http://thread.gmane.org/gmane.linux.ports.arm.kernel/462438 > - The arm64 Image is uncompressed by default, and the Elf64_Rela format uses > 24 bytes per relocation entry. This results in considerable bloat (i.e., a > couple of MBs worth of relocation data in an .init section). However, no > build time postprocessing is required, we rely fully on the toolchain to > produce the image > - We have to rely on the bootloader to supply some randomness in register x1 > upon kernel entry. Since we have no decompressor, it is simply not feasible > to collect randomness in the head.S code path before mapping the kernel and > enabling the MMU. > - The EFI_RNG_PROTOCOL that is invoked in patch #13 to supply randomness on > UEFI systems is not universally available. A QEMU/KVM firmware image that > implements a pseudo-random version is available here: > http://people.linaro.org/~ard.biesheuvel/QEMU_EFI.fd.aarch64-rng.bz2 > (requires access to PMCCNTR_EL0 and support for AES instructions) > See below for instructions how to run the pseudo-random version on real > hardware. > - Only mildly tested. Help appreciated. > > Code can be found here: > git://git.linaro.org/people/ard.biesheuvel/linux-arm.git arm64-kaslr-v2 > https://git.linaro.org/people/ard.biesheuvel/linux-arm.git/shortlog/refs/heads/arm64-kaslr-v2 > > Patch #1 updates the OF code to allow the minimum memblock physical address to > be overridden by the arch. > > Patch #2 introduces KIMAGE_VADDR as the base of the kernel virtual region. > > Patch #3 memblock_reserve()'s the .bss, swapper_pg_dir and idmap_pg_dir > individually. > > Patch #4 rewrites early_fixmap_init() so it does not rely on the linear mapping > (i.e., the use of phys_to_virt() is avoided) > > Patch #5 updates KVM on arm64 so it can deal with kernel symbols whose addresses > are not covered by the linear mapping. > > Patch #6 moves the kernel virtual mapping to the vmalloc area, along with the > module region which is kept right below it, as before. > > Patch #7 adds support for PLTs in modules so that relative branches can be > resolved via a PLT if the target is out of range. > > Patch #8 moves to the x86 version of the extable implementation so that it no > longer contains absolute addresses that require fixing up at relocation time, > but uses relative offsets instead. > > Patch #9 reverts some changes to the Image header population code so we no > longer depend on the linker to populate the header fields. This is necessary > since the R_AARCH64_ABS relocations that are emitted for these fields are not > resolved at build time for PIE executables. > > Patch #10 updates the code in head.S that needs to execute before relocation to > avoid the use of values that are subject to dynamic relocation. These values > will not be populated in PIE executables. > > Patch #11 allows the kernel Image to be loaded anywhere in physical memory, by > decoupling PHYS_OFFSET from the base of the kernel image. > > Patch #12 implements the core KASLR, by taking randomness supplied in register x1 > and using it to move the kernel inside the vmalloc area. > > Patch #13 adds an invocation of the EFI_RNG_PROTOCOL to supply randomness to the > kernel proper. I see a few other things that we'll probably want to add: - kaslr/nokaslr command line (to either ignore boot loader hint or UEFI rng) - randomization of module load address (see get_module_load_offset in arch/x86/kernel/module.c) - panic reporting of offset (see register_kernel_offset_dumper in arch/x86/kernel/setup.c) - vmcoreinfo reporting of offset (though I can't find vmcoreinfo on arm64, so maybe not, as kexec appears unimplemented) > Ard Biesheuvel (13): > of/fdt: make memblock minimum physical address arch configurable > arm64: introduce KIMAGE_VADDR as the virtual base of the kernel region > arm64: use more granular reservations for static page table > allocations > arm64: decouple early fixmap init from linear mapping > arm64: kvm: deal with kernel symbols outside of linear mapping > arm64: move kernel image to base of vmalloc area > arm64: add support for module PLTs > arm64: use relative references in exception tables > arm64: avoid R_AARCH64_ABS64 relocations for Image header fields > arm64: avoid dynamic relocations in early boot code > arm64: allow kernel Image to be loaded anywhere in physical memory > arm64: add support for relocatable kernel > arm64: efi: invoke EFI_RNG_PROTOCOL to supply KASLR randomness > > Documentation/arm64/booting.txt | 15 ++- > arch/arm/include/asm/kvm_asm.h | 2 + > arch/arm/include/asm/kvm_mmu.h | 2 + > arch/arm/kvm/arm.c | 9 +- > arch/arm/kvm/mmu.c | 12 +- > arch/arm64/Kconfig | 18 +++ > arch/arm64/Makefile | 10 +- > arch/arm64/include/asm/assembler.h | 17 ++- > arch/arm64/include/asm/boot.h | 5 + > arch/arm64/include/asm/compiler.h | 2 + > arch/arm64/include/asm/futex.h | 4 +- > arch/arm64/include/asm/kasan.h | 17 +-- > arch/arm64/include/asm/kernel-pgtable.h | 5 +- > arch/arm64/include/asm/kvm_asm.h | 21 +-- > arch/arm64/include/asm/kvm_mmu.h | 2 + > arch/arm64/include/asm/memory.h | 37 ++++-- > arch/arm64/include/asm/module.h | 11 ++ > arch/arm64/include/asm/pgtable.h | 7 - > arch/arm64/include/asm/uaccess.h | 16 +-- > arch/arm64/include/asm/virt.h | 4 - > arch/arm64/kernel/Makefile | 1 + > arch/arm64/kernel/armv8_deprecated.c | 4 +- > arch/arm64/kernel/efi-entry.S | 9 +- > arch/arm64/kernel/head.S | 133 ++++++++++++++++--- > arch/arm64/kernel/image.h | 37 ++---- > arch/arm64/kernel/module-plts.c | 137 ++++++++++++++++++++ > arch/arm64/kernel/module.c | 7 + > arch/arm64/kernel/module.lds | 4 + > arch/arm64/kernel/setup.c | 15 ++- > arch/arm64/kernel/vmlinux.lds.S | 29 +++-- > arch/arm64/kvm/debug.c | 4 +- > arch/arm64/mm/dump.c | 12 +- > arch/arm64/mm/extable.c | 102 ++++++++++++++- > arch/arm64/mm/init.c | 75 +++++++++-- > arch/arm64/mm/mmu.c | 132 +++++++------------ > drivers/firmware/efi/libstub/arm-stub.c | 1 - > drivers/firmware/efi/libstub/arm64-stub.c | 134 ++++++++++++++++--- > drivers/of/fdt.c | 5 +- > include/linux/efi.h | 5 +- > scripts/sortextable.c | 6 +- > virt/kvm/arm/vgic-v3.c | 2 +- > 41 files changed, 813 insertions(+), 257 deletions(-) > create mode 100644 arch/arm64/kernel/module-plts.c > create mode 100644 arch/arm64/kernel/module.lds > > > EFI_RNG_PROTOCOL on real hardware > ================================= > > To test whether your UEFI implements the EFI_RNG_PROTOCOL, download the > following executable and run it from the UEFI Shell: > http://people.linaro.org/~ard.biesheuvel/RngTest.efi > > FS0:\> rngtest > UEFI RNG Protocol Testing : > ---------------------------- > -- Locate UEFI RNG Protocol : [Fail - Status = Not Found] > > If your UEFI does not implement the EFI_RNG_PROTOCOL, you can download and > install the pseudo-random version that uses the generic timer and PMCCNTR_EL0 > values and permutes them using a couple of rounds of AES. > http://people.linaro.org/~ard.biesheuvel/RngDxe.efi > > NOTE: not for production!! This is a quick and dirty hack to test the KASLR > code, and is not suitable for anything else. > > FS0:\> rngdxe > FS0:\> rngtest > UEFI RNG Protocol Testing : > ---------------------------- > -- Locate UEFI RNG Protocol : [Pass] > -- Call RNG->GetInfo() interface : > >> Supported RNG Algorithm (Count = 2) : > 0) 44F0DE6E-4D8C-4045-A8C7-4DD168856B9E > 1) E43176D7-B6E8-4827-B784-7FFDC4B68561 > -- Call RNG->GetRNG() interface : > >> RNG with default algorithm : [Pass] > >> RNG with SP800-90-HMAC-256 : [Fail - Status = Unsupported] > >> RNG with SP800-90-Hash-256 : [Fail - Status = Unsupported] > >> RNG with SP800-90-CTR-256 : [Pass] > >> RNG with X9.31-3DES : [Fail - Status = Unsupported] > >> RNG with X9.31-AES : [Fail - Status = Unsupported] > >> RNG with RAW Entropy : [Pass] > -- Random Number Generation Test with default RNG Algorithm (20 Rounds): > 01) - 27 > 02) - 61E8 > 03) - 496FD8 > 04) - DDD793BF > 05) - B6C37C8E23 > 06) - 4D183C604A96 > 07) - 9363311DB61298 > 08) - 5715A7294F4E436E > 09) - F0D4D7BAA0DD52318E > 10) - C88C6EBCF4C0474D87C3 > 11) - B5594602B482A643932172 > 12) - CA7573F704B2089B726B9CF1 > 13) - A93E9451CB533DCFBA87B97C33 > 14) - 45AA7B83DB6044F7BBAB031F0D24 > 15) - 3DD7A4D61F34ADCB400B5976730DCF > 16) - 4DD168D21FAB8F59708330D6A9BEB021 > 17) - 4BBB225E61C465F174254159467E65939F > 18) - 030A156C9616337A20070941E702827DA8E1 > 19) - AB0FC11C9A4E225011382A9D164D9D55CA2B64 > 20) - 72B9B4735DC445E5DA6AF88DE965B7E87CB9A23C > Have you done any repeated boot testing? When I originally did x86 kASLR, I had a machine rebooting over and over spitting the _text line from /proc/kallsyms to the console. This both caught page table corner cases where the system was unbootable and let me run a statistical analysis of the offsets, just to make sure there wasn't any glaring error in either the RNG or the relocation. Very cool! -Kees -- Kees Cook Chrome OS & Brillo Security -- 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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