Date: Mon, 11 Jan 2016 14:07:47 -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 v3 00/21] arm64: implement support for KASLR On Mon, Jan 11, 2016 at 5:18 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. v2 and up also implement 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. I will continue cheering! :) > Changes since v2: > - Incorporated feedback from Marc Zyngier into the KVM patch (#5) > - Dropped the pgdir section and the patch that memblock_reserve()'s the kernel > sections at a smaller granularity. This is no longer necessary with the pgdir > section gone. This also fixes an issue spotted by James Morse where the fixmap > page tables are not zeroed correctly; these have been moved back to the .bss > section. > - Got rid of all ifdef'ery regarding the number of translation levels in the > changed .c files, by introducing new definitions in pgtable.h (#3, #6) > - Fixed KAsan support, which was broken by all earlier versions. > - Moved module region along with the virtually randomized kernel, so that module > addresses become unpredictable as well, and we only have to rely on veneers in > the PLTs when the module region is exhausted (which is somewhat more likely > since the module region is now shared with other uses of the vmalloc area) Just to make sure I understand: this means that the offset between kernel and modules remains static? It may still be useful to bump modules as well, just so that leaking a module address doesn't compromise the base kernel image address too. Don't block the series for this, though. It's a minor nit. :) -Kees > - Added support for the 'nokaslr' command line option. This affects the > randomization performed by the stub, and results in a warning if passed while > the bootloader also presented a random seed for virtual KASLR in register x1. > - The .text/.rodata sections of the kernel are no longer aliased in the linear > region with a writable mapping. > - Added a separate image header flag for kernel images that may be loaded at any > 2 MB aligned offset (+ TEXT_OFFSET) > - The KASLR displacement is now corrected if it results in the kernel image > intersecting a PUD/PMD boundary (4k and 16k/64k granule kernels, respectively) > - Split out UEFI stub random routines into separate patches. > - Implemented a weight based EFI random allocation routine so that each suitable > offset in available memory is equally likely to be selected (as suggested by > Kees Cook) > - Reused CONFIG_RELOCATABLE and CONFIG_RANDOMIZE_BASE instead of introducing > new Kconfig symbols to describe the same functionality. > - Reimplemented mem= logic so memory is clipped from the top first. > > 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. > - 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-v3 > https://git.linaro.org/people/ard.biesheuvel/linux-arm.git/shortlog/refs/heads/arm64-kaslr-v3 > > 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 introduces dummy pud_index() and pmd_index() macros that are intended > to be optimized away if the configured number of translation levels does not > actually use them. > > 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 introduces pte_offset_kimg(), pmd_offset_kimg() and pud_offset_kimg() > that allow statically allocated page tables (i.e., by fixmap and kasan) to be > traversed before the linear mapping is installed. > > Patch #7 moves the kernel virtual mapping to the vmalloc area, along with the > module region which is kept right below it, as before. > > Patch #8 adds support for PLTs in modules so that relative branches can be > resolved via a PLT if the target is out of range. This is required for KASLR, > since modules may be loaded far away from the core kernel. > > Patch #9 and #10 move arm64 to the a new generic relative 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 #11 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_ABS64 relocations that are emitted for these fields are not > resolved at build time for PIE executables. > > Patch #12 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 #13 allows the kernel Image to be loaded anywhere in physical memory, by > decoupling PHYS_OFFSET from the base of the kernel image. > > Patch #14 redefines SWAPPER_TABLE_SHIFT in a way that allows it to be used from > assembler code regardless of the number of configured translation levels. > > Patch #15 (from Mark Rutland) moves the ELF relocation type #defines to a > separate file so we can use it from head.S later > > Patch #16 updates scripts/sortextable.c so it accepts ET_DYN (relocatable) > executables as well as ET_EXEC (static) executables. > > Patch #17 implements the core KASLR, by taking randomness supplied in register > x1 and using it to move the kernel inside the vmalloc area. > > Patch #18 implements efi_get_random_bytes() based on the EFI_RNG_PROTOCOL > > Patch #19 implements efi_random_alloc() > > Patch #20 moves the allocation for the converted command line (UTF-16 to ASCII) > away from the base of memory. This is necessary since for parsing > > Patch #21 implements the actual KASLR, by randomizing the kernel physical > address, and passing entropy in x1 so that the kernel proper can relocate itself > virtually. > > Ard Biesheuvel (20): > of/fdt: make memblock minimum physical address arch configurable > arm64: introduce KIMAGE_VADDR as the virtual base of the kernel region > arm64: pgtable: add dummy pud_index() and pmd_index() definitions > arm64: decouple early fixmap init from linear mapping > arm64: kvm: deal with kernel symbols outside of linear mapping > arm64: pgtable: implement static [pte|pmd|pud]_offset variants > arm64: move kernel image to base of vmalloc area > arm64: add support for module PLTs > extable: add support for relative extables to search and sort routines > arm64: switch to relative 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: redefine SWAPPER_TABLE_SHIFT for use in asm code > scripts/sortextable: add support for ET_DYN binaries > arm64: add support for a relocatable kernel and KASLR > efi: stub: implement efi_get_random_bytes() based on EFI_RNG_PROTOCOL > efi: stub: add implementation of efi_random_alloc() > efi: stub: use high allocation for converted command line > arm64: efi: invoke EFI_RNG_PROTOCOL to supply KASLR randomness > > Mark Rutland (1): > arm64: split elf relocs into a separate header. > > Documentation/arm64/booting.txt | 34 ++++- > arch/arm/include/asm/kvm_asm.h | 2 + > arch/arm/include/asm/kvm_mmu.h | 2 + > arch/arm/kvm/arm.c | 5 +- > arch/arm/kvm/mmu.c | 8 +- > arch/arm64/Kconfig | 40 +++++ > arch/arm64/Makefile | 10 +- > arch/arm64/include/asm/assembler.h | 30 +++- > arch/arm64/include/asm/boot.h | 6 + > arch/arm64/include/asm/elf.h | 54 +------ > arch/arm64/include/asm/elf_relocs.h | 75 ++++++++++ > arch/arm64/include/asm/futex.h | 12 +- > arch/arm64/include/asm/kasan.h | 20 +-- > arch/arm64/include/asm/kernel-pgtable.h | 20 ++- > arch/arm64/include/asm/kvm_asm.h | 19 ++- > arch/arm64/include/asm/kvm_host.h | 8 +- > arch/arm64/include/asm/kvm_mmu.h | 2 + > arch/arm64/include/asm/memory.h | 38 +++-- > arch/arm64/include/asm/module.h | 11 ++ > arch/arm64/include/asm/pgtable.h | 22 ++- > arch/arm64/include/asm/uaccess.h | 30 ++-- > arch/arm64/include/asm/virt.h | 4 - > arch/arm64/include/asm/word-at-a-time.h | 7 +- > arch/arm64/kernel/Makefile | 1 + > arch/arm64/kernel/armv8_deprecated.c | 7 +- > arch/arm64/kernel/efi-entry.S | 9 +- > arch/arm64/kernel/head.S | 155 +++++++++++++++++--- > arch/arm64/kernel/image.h | 37 ++--- > arch/arm64/kernel/module-plts.c | 137 +++++++++++++++++ > arch/arm64/kernel/module.c | 15 +- > arch/arm64/kernel/module.lds | 4 + > arch/arm64/kernel/setup.c | 44 +++++- > arch/arm64/kernel/vmlinux.lds.S | 13 +- > arch/arm64/kvm/debug.c | 1 + > arch/arm64/kvm/hyp.S | 6 +- > arch/arm64/mm/dump.c | 12 +- > arch/arm64/mm/extable.c | 2 +- > arch/arm64/mm/init.c | 91 ++++++++++-- > arch/arm64/mm/kasan_init.c | 21 ++- > arch/arm64/mm/mmu.c | 95 +++++++----- > arch/x86/include/asm/efi.h | 2 + > drivers/firmware/efi/libstub/Makefile | 2 +- > drivers/firmware/efi/libstub/arm-stub.c | 17 ++- > drivers/firmware/efi/libstub/arm64-stub.c | 67 +++++++-- > drivers/firmware/efi/libstub/efi-stub-helper.c | 24 ++- > drivers/firmware/efi/libstub/efistub.h | 9 ++ > drivers/firmware/efi/libstub/random.c | 120 +++++++++++++++ > drivers/of/fdt.c | 5 +- > include/linux/efi.h | 5 +- > lib/extable.c | 50 +++++-- > scripts/sortextable.c | 10 +- > 51 files changed, 1111 insertions(+), 309 deletions(-) > create mode 100644 arch/arm64/include/asm/elf_relocs.h > create mode 100644 arch/arm64/kernel/module-plts.c > create mode 100644 arch/arm64/kernel/module.lds > create mode 100644 drivers/firmware/efi/libstub/random.c > > 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 -- Kees Cook Chrome OS & Brillo Security
Powered by blists - more mailing lists
Confused about mailing lists and their use? Read about mailing lists on Wikipedia and check out these guidelines on proper formatting of your messages.