On 10/12/19 3:47 pm, Daniel Axtens wrote: > KASAN support on powerpc64 is challenging: > > - We want to be able to support inline instrumentation so as to be > able to catch global and stack issues. > > - We run some code in real mode after boot, most notably a lot of > KVM code. We'd like to be able to instrument this. > > [For those not immersed in ppc64, in real mode, the top nibble or > 2 bits (depending on radix/hash mmu) of the address is ignored. The > linear mapping is placed at 0xc000000000000000. This means that a > pointer to part of the linear mapping will work both in real mode, > where it will be interpreted as a physical address of the form > 0x000..., and out of real mode, where it will go via the linear > mapping.] > > - Inline instrumentation requires a fixed offset. > > - Because of our running things in real mode, the offset has to > point to valid memory both in and out of real mode. > > This makes finding somewhere to put the KASAN shadow region challenging. > > One approach is just to give up on inline instrumentation and override > the address->shadow calculation. This way we can delay all checking > until after we get everything set up to our satisfaction. However, > we'd really like to do better. > > What we can do - if we know _at compile time_ how much contiguous > physical memory we have - is to set aside the top 1/8th of the memory > and use that. This is a big hammer (hence the "heavyweight" name) and > comes with 3 big consequences: > > - kernels will simply fail to boot on machines with less memory than > specified when compiling. > > - kernels running on machines with more memory than specified when > compiling will simply ignore the extra memory. > > - there's no nice way to handle physically discontiguous memory, so > you are restricted to the first physical memory block. > > If you can bear all this, you get full support for KASAN. > > Despite the limitations, it can still find bugs, > e.g. http://patchwork.ozlabs.org/patch/1103775/ > > The current implementation is Radix only. > > Massive thanks to mpe, who had the idea for the initial design. > > Signed-off-by: Daniel Axtens <dja@xxxxxxxxxx> > > --- > Changes since v1: > - Landed kasan vmalloc support upstream > - Lots of feedback from Christophe. > > Changes since the rfc: > > - Boots real and virtual hardware, kvm works. > > - disabled reporting when we're checking the stack for exception > frames. The behaviour isn't wrong, just incompatible with KASAN. > > - Documentation! > > - Dropped old module stuff in favour of KASAN_VMALLOC. > > The bugs with ftrace and kuap were due to kernel bloat pushing > prom_init calls to be done via the plt. Because we did not have > a relocatable kernel, and they are done very early, this caused > everything to explode. Compile with CONFIG_RELOCATABLE! > --- > Documentation/dev-tools/kasan.rst | 8 +- > Documentation/powerpc/kasan.txt | 102 +++++++++++++++++- > arch/powerpc/Kconfig | 3 + > arch/powerpc/Kconfig.debug | 21 ++++ > arch/powerpc/Makefile | 11 ++ > arch/powerpc/include/asm/kasan.h | 20 +++- > arch/powerpc/kernel/process.c | 8 ++ > arch/powerpc/kernel/prom.c | 59 +++++++++- > arch/powerpc/mm/kasan/Makefile | 3 +- > .../mm/kasan/{kasan_init_32.c => init_32.c} | 0 > arch/powerpc/mm/kasan/init_book3s_64.c | 67 ++++++++++++ > 11 files changed, 293 insertions(+), 9 deletions(-) > rename arch/powerpc/mm/kasan/{kasan_init_32.c => init_32.c} (100%) > create mode 100644 arch/powerpc/mm/kasan/init_book3s_64.c > > diff --git a/Documentation/dev-tools/kasan.rst b/Documentation/dev-tools/kasan.rst > index 4af2b5d2c9b4..d99dc580bc11 100644 > --- a/Documentation/dev-tools/kasan.rst > +++ b/Documentation/dev-tools/kasan.rst > @@ -22,8 +22,9 @@ global variables yet. > Tag-based KASAN is only supported in Clang and requires version 7.0.0 or later. > > Currently generic KASAN is supported for the x86_64, arm64, xtensa and s390 > -architectures. It is also supported on 32-bit powerpc kernels. Tag-based KASAN > -is supported only on arm64. > +architectures. It is also supported on powerpc, for 32-bit kernels, and for > +64-bit kernels running under the Radix MMU. Tag-based KASAN is supported only > +on arm64. > > Usage > ----- > @@ -256,7 +257,8 @@ CONFIG_KASAN_VMALLOC > ~~~~~~~~~~~~~~~~~~~~ > > With ``CONFIG_KASAN_VMALLOC``, KASAN can cover vmalloc space at the > -cost of greater memory usage. Currently this is only supported on x86. > +cost of greater memory usage. Currently this is optional on x86, and > +required on 64-bit powerpc. > > This works by hooking into vmalloc and vmap, and dynamically > allocating real shadow memory to back the mappings. > diff --git a/Documentation/powerpc/kasan.txt b/Documentation/powerpc/kasan.txt > index a85ce2ff8244..d6e7a415195c 100644 > --- a/Documentation/powerpc/kasan.txt > +++ b/Documentation/powerpc/kasan.txt > @@ -1,4 +1,4 @@ > -KASAN is supported on powerpc on 32-bit only. > +KASAN is supported on powerpc on 32-bit and 64-bit Radix only. > > 32 bit support > ============== > @@ -10,3 +10,103 @@ fixmap area and occupies one eighth of the total kernel virtual memory space. > > Instrumentation of the vmalloc area is not currently supported, but modules > are. > + > +64 bit support > +============== > + > +Currently, only the radix MMU is supported. There have been versions for Book3E > +processors floating around on the mailing list, but nothing has been merged. > + > +KASAN support on Book3S is a bit tricky to get right: > + > + - We want to be able to support inline instrumentation so as to be able to > + catch global and stack issues. > + > + - Inline instrumentation requires a fixed offset. > + > + - We run a lot of code in real mode. Most notably a lot of KVM runs in real > + mode, and we'd like to be able to instrument it. > + > + - Because we run code in real mode after boot, the offset has to point to > + valid memory both in and out of real mode. > + > +One approach is just to give up on inline instrumentation. This way we can > +delay all checks until after we get everything set up correctly. However, we'd > +really like to do better. > + > +If we know _at compile time_ how much contiguous physical memory we have, we > +can set aside the top 1/8th of the first block of physical memory and use > +that. This is a big hammer and comes with 3 big consequences: > + > + - there's no nice way to handle physically discontiguous memory, so > + you are restricted to the first physical memory block. > + > + - kernels will simply fail to boot on machines with less memory than specified > + when compiling. > + > + - kernels running on machines with more memory than specified when compiling > + will simply ignore the extra memory. > + > +If you can live with this, you get full support for KASAN. > + > +Tips > +---- > + > + - Compile with CONFIG_RELOCATABLE. > + > + In development, we found boot hangs when building with ftrace and KUAP > + on. These ended up being due to kernel bloat pushing prom_init calls to be > + done via the PLT. Because we did not have a relocatable kernel, and they are > + done very early, this caused us to jump off into somewhere invalid. Enabling > + relocation fixes this. > + > +NUMA/discontiguous physical memory > +---------------------------------- > + > +We currently cannot really deal with discontiguous physical memory. You are > +restricted to the physical memory that is contiguous from physical address > +zero, and must specify the size of that memory, not total memory, when > +configuring your kernel. > + > +Discontiguous memory can occur when you have a machine with memory spread > +across multiple nodes. For example, on a Talos II with 64GB of RAM: > + > + - 32GB runs from 0x0 to 0x0000_0008_0000_0000, > + - then there's a gap, > + - then the final 32GB runs from 0x0000_2000_0000_0000 to 0x0000_2008_0000_0000 > + > +This can create _significant_ issues: > + > + - If we try to treat the machine as having 64GB of _contiguous_ RAM, we would > + assume that ran from 0x0 to 0x0000_0010_0000_0000. We'd then reserve the > + last 1/8th - 0x0000_000e_0000_0000 to 0x0000_0010_0000_0000 as the shadow > + region. But when we try to access any of that, we'll try to access pages > + that are not physically present. > + If we reserved memory for KASAN from each node (discontig region), we might survive this no? May be we need NUMA aware KASAN? That might be a generic change, just thinking out loud. > + - If we try to base the shadow region size on the top address, we'll need to > + reserve 0x2008_0000_0000 / 8 = 0x0401_0000_0000 bytes = 4100 GB of memory, > + which will clearly not work on a system with 64GB of RAM. > + > +Therefore, you are restricted to the memory in the node starting at 0x0. For > +this system, that's 32GB. If you specify a contiguous physical memory size > +greater than the size of the first contiguous region of memory, the system will > +be unable to boot or even print an error message warning you. > + > +You can determine the layout of your system's memory by observing the messages > +that the Radix MMU prints on boot. The Talos II discussed earlier has: > + > +radix-mmu: Mapped 0x0000000000000000-0x0000000040000000 with 1.00 GiB pages (exec) > +radix-mmu: Mapped 0x0000000040000000-0x0000000800000000 with 1.00 GiB pages > +radix-mmu: Mapped 0x0000200000000000-0x0000200800000000 with 1.00 GiB pages > + > +As discussed, you'd configure this system for 32768 MB. > + > +Another system prints: > + > +radix-mmu: Mapped 0x0000000000000000-0x0000000040000000 with 1.00 GiB pages (exec) > +radix-mmu: Mapped 0x0000000040000000-0x0000002000000000 with 1.00 GiB pages > +radix-mmu: Mapped 0x0000200000000000-0x0000202000000000 with 1.00 GiB pages > + > +This machine has more memory: 0x0000_0040_0000_0000 total, but only > +0x0000_0020_0000_0000 is physically contiguous from zero, so we'd configure the > +kernel for 131072 MB of physically contiguous memory. > diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig > index 1ec34e16ed65..f68650f14e61 100644 > --- a/arch/powerpc/Kconfig > +++ b/arch/powerpc/Kconfig > @@ -173,6 +173,9 @@ config PPC > select HAVE_ARCH_HUGE_VMAP if PPC_BOOK3S_64 && PPC_RADIX_MMU > select HAVE_ARCH_JUMP_LABEL > select HAVE_ARCH_KASAN if PPC32 > + select HAVE_ARCH_KASAN if PPC_BOOK3S_64 && PPC_RADIX_MMU > + select HAVE_ARCH_KASAN_VMALLOC if PPC_BOOK3S_64 > + select KASAN_VMALLOC if KASAN && PPC_BOOK3S_64 > select HAVE_ARCH_KGDB > select HAVE_ARCH_MMAP_RND_BITS > select HAVE_ARCH_MMAP_RND_COMPAT_BITS if COMPAT > diff --git a/arch/powerpc/Kconfig.debug b/arch/powerpc/Kconfig.debug > index 4e1d39847462..90bb48455cb8 100644 > --- a/arch/powerpc/Kconfig.debug > +++ b/arch/powerpc/Kconfig.debug > @@ -394,6 +394,27 @@ config PPC_FAST_ENDIAN_SWITCH > help > If you're unsure what this is, say N. > > +config PHYS_MEM_SIZE_FOR_KASAN > + int "Contiguous physical memory size for KASAN (MB)" if KASAN && PPC_BOOK3S_64 > + default 0 > + help > + > + To get inline instrumentation support for KASAN on 64-bit Book3S > + machines, you need to know how much contiguous physical memory your > + system has. A shadow offset will be calculated based on this figure, > + which will be compiled in to the kernel. KASAN will use this offset > + to access its shadow region, which is used to verify memory accesses. > + > + If you attempt to boot on a system with less memory than you specify > + here, your system will fail to boot very early in the process. If you > + boot on a system with more memory than you specify, the extra memory > + will wasted - it will be reserved and not used. > + > + For systems with discontiguous blocks of physical memory, specify the > + size of the block starting at 0x0. You can determine this by looking > + at the memory layout info printed to dmesg by the radix MMU code > + early in boot. See Documentation/powerpc/kasan.txt. > + > config KASAN_SHADOW_OFFSET > hex > depends on KASAN > diff --git a/arch/powerpc/Makefile b/arch/powerpc/Makefile > index f35730548e42..eff693527462 100644 > --- a/arch/powerpc/Makefile > +++ b/arch/powerpc/Makefile > @@ -230,6 +230,17 @@ ifdef CONFIG_476FPE_ERR46 > -T $(srctree)/arch/powerpc/platforms/44x/ppc476_modules.lds > endif > > +ifdef CONFIG_PPC_BOOK3S_64 > +# The KASAN shadow offset is such that linear map (0xc000...) is shadowed by > +# the last 8th of linearly mapped physical memory. This way, if the code uses > +# 0xc addresses throughout, accesses work both in in real mode (where the top > +# 2 bits are ignored) and outside of real mode. > +# > +# 0xc000000000000000 >> 3 = 0xa800000000000000 = 12105675798371893248 > +KASAN_SHADOW_OFFSET = $(shell echo 7 \* 1024 \* 1024 \* $(CONFIG_PHYS_MEM_SIZE_FOR_KASAN) / 8 + 12105675798371893248 | bc) > +KBUILD_CFLAGS += -DKASAN_SHADOW_OFFSET=$(KASAN_SHADOW_OFFSET)UL > +endif > + > # No AltiVec or VSX instructions when building kernel > KBUILD_CFLAGS += $(call cc-option,-mno-altivec) > KBUILD_CFLAGS += $(call cc-option,-mno-vsx) > diff --git a/arch/powerpc/include/asm/kasan.h b/arch/powerpc/include/asm/kasan.h > index 296e51c2f066..98d995bc9b5e 100644 > --- a/arch/powerpc/include/asm/kasan.h > +++ b/arch/powerpc/include/asm/kasan.h > @@ -14,13 +14,20 @@ > > #ifndef __ASSEMBLY__ > > -#include <asm/page.h> > +#ifdef CONFIG_KASAN > +void kasan_init(void); > +#else > +static inline void kasan_init(void) { } > +#endif > > #define KASAN_SHADOW_SCALE_SHIFT 3 > > #define KASAN_SHADOW_START (KASAN_SHADOW_OFFSET + \ > (PAGE_OFFSET >> KASAN_SHADOW_SCALE_SHIFT)) > > +#ifdef CONFIG_PPC32 > +#include <asm/page.h> > + > #define KASAN_SHADOW_OFFSET ASM_CONST(CONFIG_KASAN_SHADOW_OFFSET) > > #define KASAN_SHADOW_END 0UL > @@ -30,11 +37,18 @@ > #ifdef CONFIG_KASAN > void kasan_early_init(void); > void kasan_mmu_init(void); > -void kasan_init(void); > #else > -static inline void kasan_init(void) { } > static inline void kasan_mmu_init(void) { } > #endif > +#endif > + > +#ifdef CONFIG_PPC_BOOK3S_64 > +#include <asm/pgtable.h> > + > +#define KASAN_SHADOW_SIZE ((u64)CONFIG_PHYS_MEM_SIZE_FOR_KASAN * \ > + 1024 * 1024 * 1 / 8) > + > +#endif /* CONFIG_PPC_BOOK3S_64 */ > > #endif /* __ASSEMBLY */ > #endif > diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c > index 4df94b6e2f32..c60ff299f39b 100644 > --- a/arch/powerpc/kernel/process.c > +++ b/arch/powerpc/kernel/process.c > @@ -2081,7 +2081,14 @@ void show_stack(struct task_struct *tsk, unsigned long *stack) > /* > * See if this is an exception frame. > * We look for the "regshere" marker in the current frame. > + * > + * KASAN may complain about this. If it is an exception frame, > + * we won't have unpoisoned the stack in asm when we set the > + * exception marker. If it's not an exception frame, who knows > + * how things are laid out - the shadow could be in any state > + * at all. Just disable KASAN reporting for now. > */ > + kasan_disable_current(); > if (validate_sp(sp, tsk, STACK_INT_FRAME_SIZE) > && stack[STACK_FRAME_MARKER] == STACK_FRAME_REGS_MARKER) { > struct pt_regs *regs = (struct pt_regs *) > @@ -2091,6 +2098,7 @@ void show_stack(struct task_struct *tsk, unsigned long *stack) > regs->trap, (void *)regs->nip, (void *)lr); > firstframe = 1; > } > + kasan_enable_current(); > > sp = newsp; > } while (count++ < kstack_depth_to_print); > diff --git a/arch/powerpc/kernel/prom.c b/arch/powerpc/kernel/prom.c > index 6620f37abe73..b32036f61cad 100644 > --- a/arch/powerpc/kernel/prom.c > +++ b/arch/powerpc/kernel/prom.c > @@ -72,6 +72,7 @@ unsigned long tce_alloc_start, tce_alloc_end; > u64 ppc64_rma_size; > #endif > static phys_addr_t first_memblock_size; > +static phys_addr_t top_phys_addr; > static int __initdata boot_cpu_count; > > static int __init early_parse_mem(char *p) > @@ -449,6 +450,21 @@ static bool validate_mem_limit(u64 base, u64 *size) > { > u64 max_mem = 1UL << (MAX_PHYSMEM_BITS); > > +#ifdef CONFIG_KASAN > + /* > + * To handle the NUMA/discontiguous memory case, don't allow a block > + * to be added if it falls completely beyond the configured physical > + * memory. > + * > + * See Documentation/powerpc/kasan.txt > + */ > + if (base >= (u64)CONFIG_PHYS_MEM_SIZE_FOR_KASAN * 1024 * 1024) { > + pr_warn("KASAN: not adding mem block at %llx (size %llx)", > + base, *size); > + return false; > + } > +#endif > + > if (base >= max_mem) > return false; > if ((base + *size) > max_mem) > @@ -572,8 +588,11 @@ void __init early_init_dt_add_memory_arch(u64 base, u64 size) > > /* Add the chunk to the MEMBLOCK list */ > if (add_mem_to_memblock) { > - if (validate_mem_limit(base, &size)) > + if (validate_mem_limit(base, &size)) { > memblock_add(base, size); > + if (base + size > top_phys_addr) > + top_phys_addr = base + size; > + } > } > } > > @@ -613,6 +632,8 @@ static void __init early_reserve_mem_dt(void) > static void __init early_reserve_mem(void) > { > __be64 *reserve_map; > + phys_addr_t kasan_shadow_start; > + phys_addr_t kasan_memory_size; > > reserve_map = (__be64 *)(((unsigned long)initial_boot_params) + > fdt_off_mem_rsvmap(initial_boot_params)); > @@ -651,6 +672,42 @@ static void __init early_reserve_mem(void) > return; > } > #endif > + > + if (IS_ENABLED(CONFIG_KASAN) && IS_ENABLED(CONFIG_PPC_BOOK3S_64)) { > + kasan_memory_size = > + ((phys_addr_t)CONFIG_PHYS_MEM_SIZE_FOR_KASAN << 20); > + > + if (top_phys_addr < kasan_memory_size) { > + /* > + * We are doomed. Attempts to call e.g. panic() are > + * likely to fail because they call out into > + * instrumented code, which will almost certainly > + * access memory beyond the end of physical > + * memory. Hang here so that at least the NIP points > + * somewhere that will help you debug it if you look at > + * it in qemu. > + */ > + while (true) > + ; Again with the right hooks in check_memory_region_inline() these are recoverable, or so I think > + } else if (top_phys_addr > kasan_memory_size) { > + /* print a biiiig warning in hopes people notice */ > + pr_err("===========================================\n" > + "Physical memory exceeds compiled-in maximum!\n" > + "This kernel was compiled for KASAN with %u MB physical memory.\n" > + "The actual physical memory detected is %llu MB.\n" > + "Memory above the compiled limit will not be used!\n" > + "===========================================\n", > + CONFIG_PHYS_MEM_SIZE_FOR_KASAN, > + top_phys_addr / (1024 * 1024)); > + } > + > + kasan_shadow_start = _ALIGN_DOWN(kasan_memory_size * 7 / 8, > + PAGE_SIZE); > + DBG("reserving %llx -> %llx for KASAN", > + kasan_shadow_start, top_phys_addr); > + memblock_reserve(kasan_shadow_start, > + top_phys_addr - kasan_shadow_start); > + } > } > > #ifdef CONFIG_PPC_TRANSACTIONAL_MEM > diff --git a/arch/powerpc/mm/kasan/Makefile b/arch/powerpc/mm/kasan/Makefile > index 6577897673dd..f02b15c78e4d 100644 > --- a/arch/powerpc/mm/kasan/Makefile > +++ b/arch/powerpc/mm/kasan/Makefile > @@ -2,4 +2,5 @@ > > KASAN_SANITIZE := n > > -obj-$(CONFIG_PPC32) += kasan_init_32.o > +obj-$(CONFIG_PPC32) += init_32.o > +obj-$(CONFIG_PPC_BOOK3S_64) += init_book3s_64.o > diff --git a/arch/powerpc/mm/kasan/kasan_init_32.c b/arch/powerpc/mm/kasan/init_32.c > similarity index 100% > rename from arch/powerpc/mm/kasan/kasan_init_32.c > rename to arch/powerpc/mm/kasan/init_32.c > diff --git a/arch/powerpc/mm/kasan/init_book3s_64.c b/arch/powerpc/mm/kasan/init_book3s_64.c > new file mode 100644 > index 000000000000..43e9252c8bd3 > --- /dev/null > +++ b/arch/powerpc/mm/kasan/init_book3s_64.c > @@ -0,0 +1,67 @@ > +// SPDX-License-Identifier: GPL-2.0 > +/* > + * KASAN for 64-bit Book3S powerpc > + * > + * Copyright (C) 2019 IBM Corporation > + * Author: Daniel Axtens <dja@xxxxxxxxxx> > + */ > + > +#define DISABLE_BRANCH_PROFILING > + > +#include <linux/kasan.h> > +#include <linux/printk.h> > +#include <linux/sched/task.h> > +#include <asm/pgalloc.h> > + > +void __init kasan_init(void) > +{ > + int i; > + void *k_start = kasan_mem_to_shadow((void *)RADIX_KERN_VIRT_START); > + void *k_end = kasan_mem_to_shadow((void *)RADIX_VMEMMAP_END); > + > + pte_t pte = __pte(__pa(kasan_early_shadow_page) | > + pgprot_val(PAGE_KERNEL) | _PAGE_PTE); > + > + if (!early_radix_enabled()) > + panic("KASAN requires radix!"); > + I think this is avoidable, we could use a static key for disabling kasan in the generic code. I wonder what happens if someone tries to boot this image on a Power8 box and keeps panic'ing with no easy way of recovering. > + for (i = 0; i < PTRS_PER_PTE; i++) > + __set_pte_at(&init_mm, (unsigned long)kasan_early_shadow_page, > + &kasan_early_shadow_pte[i], pte, 0); > + > + for (i = 0; i < PTRS_PER_PMD; i++) > + pmd_populate_kernel(&init_mm, &kasan_early_shadow_pmd[i], > + kasan_early_shadow_pte); > + > + for (i = 0; i < PTRS_PER_PUD; i++) > + pud_populate(&init_mm, &kasan_early_shadow_pud[i], > + kasan_early_shadow_pmd); > + > + memset(kasan_mem_to_shadow((void *)PAGE_OFFSET), KASAN_SHADOW_INIT, > + KASAN_SHADOW_SIZE); > + > + kasan_populate_early_shadow( > + kasan_mem_to_shadow((void *)RADIX_KERN_VIRT_START), > + kasan_mem_to_shadow((void *)RADIX_VMALLOC_START)); > + > + /* leave a hole here for vmalloc */ > + > + kasan_populate_early_shadow( > + kasan_mem_to_shadow((void *)RADIX_VMALLOC_END), > + kasan_mem_to_shadow((void *)RADIX_VMEMMAP_END)); > + > + flush_tlb_kernel_range((unsigned long)k_start, (unsigned long)k_end); > + > + /* mark early shadow region as RO and wipe */ > + pte = __pte(__pa(kasan_early_shadow_page) | > + pgprot_val(PAGE_KERNEL_RO) | _PAGE_PTE); > + for (i = 0; i < PTRS_PER_PTE; i++) > + __set_pte_at(&init_mm, (unsigned long)kasan_early_shadow_page, > + &kasan_early_shadow_pte[i], pte, 0); > + > + memset(kasan_early_shadow_page, 0, PAGE_SIZE); > + > + /* Enable error messages */ > + init_task.kasan_depth = 0; > + pr_info("KASAN init done (64-bit Book3S heavyweight mode)\n"); > +} > NOTE: I can't test any of these, well may be with qemu, let me see if I can spin the series and provide more feedback Balbir
