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SubjectRe: [PATCH v3 3/3] powerpc: Book3S 64-bit "heavyweight" KASAN support
Date
Hi Christophe,

I'm working through your feedback, thank you. Regarding this one:

>> --- 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();
>
> If this is really a concern for all targets including PPC32, should it
> be a separate patch with a Fixes: tag to be applied back in stable as well ?

I've managed to repro this by commening out the kasan_disable/enable
lines, and just booting in qemu without a disk attached:

sudo qemu-system-ppc64 -accel kvm -m 2G -M pseries -cpu power9 -kernel ./vmlinux -nographic -chardev stdio,id=charserial0,mux=on -device spapr-vty,chardev=charserial0,reg=0x30000000 -mon chardev=charserial0,mode=readline -nodefaults -smp 2

...

[ 0.210740] Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(0,0)
[ 0.210789] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.5.0-rc1-next-20191213-16824-g469a24fbdb34 #12
[ 0.210844] Call Trace:
[ 0.210866] [c00000006a4839b0] [c000000001f74f48] dump_stack+0xfc/0x154 (unreliable)
[ 0.210915] [c00000006a483a00] [c00000000025411c] panic+0x258/0x59c
[ 0.210958] [c00000006a483aa0] [c0000000024870b0] mount_block_root+0x648/0x7ac
[ 0.211005] ==================================================================
[ 0.211054] BUG: KASAN: stack-out-of-bounds in show_stack+0x438/0x580
[ 0.211095] Read of size 8 at addr c00000006a483b00 by task swapper/0/1
[ 0.211134]
[ 0.211152] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.5.0-rc1-next-20191213-16824-g469a24fbdb34 #12
[ 0.211207] Call Trace:
[ 0.211225] [c00000006a483680] [c000000001f74f48] dump_stack+0xfc/0x154 (unreliable)
[ 0.211274] [c00000006a4836d0] [c0000000008f877c] print_address_description.isra.10+0x7c/0x470
[ 0.211330] [c00000006a483760] [c0000000008f8e7c] __kasan_report+0x1bc/0x244
[ 0.211380] [c00000006a483830] [c0000000008f6eb8] kasan_report+0x18/0x30
[ 0.211422] [c00000006a483850] [c0000000008fa5d4] __asan_report_load8_noabort+0x24/0x40
[ 0.211471] [c00000006a483870] [c00000000003d448] show_stack+0x438/0x580
[ 0.211512] [c00000006a4839b0] [c000000001f74f48] dump_stack+0xfc/0x154
[ 0.211553] [c00000006a483a00] [c00000000025411c] panic+0x258/0x59c
[ 0.211595] [c00000006a483aa0] [c0000000024870b0] mount_block_root+0x648/0x7ac
[ 0.211644] [c00000006a483be0] [c000000002487784] prepare_namespace+0x1ec/0x240
[ 0.211694] [c00000006a483c60] [c00000000248669c] kernel_init_freeable+0x7f4/0x870
[ 0.211745] [c00000006a483da0] [c000000000011f30] kernel_init+0x3c/0x15c
[ 0.211787] [c00000006a483e20] [c00000000000bebc] ret_from_kernel_thread+0x5c/0x80
[ 0.211834]
[ 0.211851] Allocated by task 0:
[ 0.211878] save_stack+0x2c/0xe0
[ 0.211904] __kasan_kmalloc.isra.16+0x11c/0x150
[ 0.211937] kmem_cache_alloc_node+0x114/0x3b0
[ 0.211971] copy_process+0x5b8/0x6410
[ 0.211996] _do_fork+0x130/0xbf0
[ 0.212022] kernel_thread+0xdc/0x130
[ 0.212047] rest_init+0x44/0x184
[ 0.212072] start_kernel+0x77c/0x7dc
[ 0.212098] start_here_common+0x1c/0x20
[ 0.212122]
[ 0.212139] Freed by task 0:
[ 0.212163] (stack is not available)
[ 0.212187]
[ 0.212205] The buggy address belongs to the object at c00000006a480000
[ 0.212205] which belongs to the cache thread_stack of size 16384
[ 0.212285] The buggy address is located 15104 bytes inside of
[ 0.212285] 16384-byte region [c00000006a480000, c00000006a484000)
[ 0.212356] The buggy address belongs to the page:
[ 0.212391] page:c00c0000001a9200 refcount:1 mapcount:0 mapping:c00000006a019e00 index:0x0 compound_mapcount: 0
[ 0.212455] raw: 007ffff000010200 5deadbeef0000100 5deadbeef0000122 c00000006a019e00
[ 0.212504] raw: 0000000000000000 0000000000100010 00000001ffffffff 0000000000000000
[ 0.212551] page dumped because: kasan: bad access detected
[ 0.212583]
[ 0.212600] addr c00000006a483b00 is located in stack of task swapper/0/1 at offset 0 in frame:
[ 0.212656] mount_block_root+0x0/0x7ac
[ 0.212681]
[ 0.212698] this frame has 1 object:
[ 0.212722] [32, 64) 'b'
[ 0.212723]
[ 0.212755] Memory state around the buggy address:
[ 0.212788] c00000006a483a00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
[ 0.212836] c00000006a483a80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
[ 0.212884] >c00000006a483b00: f1 f1 f1 f1 00 00 00 00 f3 f3 f3 f3 00 00 00 00
[ 0.212931] ^
[ 0.212957] c00000006a483b80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
[ 0.213005] c00000006a483c00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
[ 0.213052] ==================================================================
[ 0.213100] Disabling lock debugging due to kernel taint
[ 0.213134] [c00000006a483be0] [c000000002487784] prepare_namespace+0x1ec/0x240
[ 0.213182] [c00000006a483c60] [c00000000248669c] kernel_init_freeable+0x7f4/0x870
[ 0.213231] [c00000006a483da0] [c000000000011f30] kernel_init+0x3c/0x15c
[ 0.213272] [c00000006a483e20] [c00000000000bebc] ret_from_kernel_thread+0x5c/0x80

Is that something that reproduces on ppc32?

I don't see it running the test_kasan tests, so I guess that matches up
with your experience.

Regards,
Daniel



>
>>
>> sp = newsp;
>> } while (count++ < kstack_depth_to_print);
>> diff --git a/arch/powerpc/kernel/prom.c b/arch/powerpc/kernel/prom.c
>> index 6620f37abe73..d994c7c39c8d 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 +450,26 @@ static bool validate_mem_limit(u64 base, u64 *size)
>> {
>> u64 max_mem = 1UL << (MAX_PHYSMEM_BITS);
>>
>> + /*
>> + * To handle the NUMA/discontiguous memory case, don't allow a block
>> + * to be added if it falls completely beyond the configured physical
>> + * memory. Print an informational message.
>> + *
>> + * Frustratingly we also see this with qemu - it seems to split the
>> + * specified memory into a number of smaller blocks. If this happens
>> + * under qemu, it probably represents misconfiguration. So we want
>> + * the message to be noticeable, but not shouty.
>> + *
>> + * See Documentation/powerpc/kasan.txt
>> + */
>> + if (IS_ENABLED(CONFIG_KASAN) &&
>> + (base >= ((u64)CONFIG_PHYS_MEM_SIZE_FOR_KASAN << 20))) {
>> + pr_warn("KASAN: not adding memory block at %llx (size %llx)\n"
>> + "This could be due to discontiguous memory or kernel misconfiguration.",
>> + base, *size);
>> + return false;
>> + }
>> +
>> if (base >= max_mem)
>> return false;
>> if ((base + *size) > max_mem)
>> @@ -572,8 +593,11 @@ 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;
>> + }
>
> Can we use max() here ? Something like
>
> top_phys_addr = max(base + size, top_phys_addr);
>
>> }
>> }
>>
>> @@ -613,6 +637,8 @@ 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 +677,42 @@ 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. We shouldn't even be able to get this
>> + * far, but we do in qemu. If we continue and turn
>> + * relocations on, we'll take fatal page faults for
>> + * memory that's not physically present. Instead,
>> + * panic() here: it will be saved to __log_buf even if
>> + * it doesn't get printed to the console.
>> + */
>> + panic("Tried to book a KASAN kernel configured for %u MB with only %llu MB! Aborting.",
>
> book ==> boot ?
>
>> + CONFIG_PHYS_MEM_SIZE_FOR_KASAN,
>> + (u64)(top_phys_addr >> 20));
>> + } 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 physical memory detected is at least %llu MB.\n"
>> + "Memory above the compiled limit will not be used!\n"
>> + "===========================================\n",
>> + CONFIG_PHYS_MEM_SIZE_FOR_KASAN,
>> + (u64)(top_phys_addr >> 20));
>> + }
>> +
>> + kasan_shadow_start = _ALIGN_DOWN(kasan_memory_size * 7 / 8,
>> + PAGE_SIZE);
>
> Can't this fit on a single line ? powerpc allows 90 chars.
>
>> + DBG("reserving %llx -> %llx for KASAN",
>> + kasan_shadow_start, top_phys_addr);
>> + memblock_reserve(kasan_shadow_start,
>> + top_phys_addr - kasan_shadow_start);
>
> Same ?
>
>> + }
>> }
>>
>> #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
>
> Shouldn't we do ppc32 name change in another patch ?
>
>> +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..f961e96be136
>> --- /dev/null
>> +++ b/arch/powerpc/mm/kasan/init_book3s_64.c
>> @@ -0,0 +1,72 @@
>> +// SPDX-License-Identifier: GPL-2.0
>> +/*
>> + * KASAN for 64-bit Book3S powerpc
>> + *
>> + * Copyright (C) 2019 IBM Corporation
>> + * Author: Daniel Axtens <dja@axtens.net>
>> + */
>> +
>> +#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);
> Can't we do something with existing helpers ? Something like:
>
> pte = pte_mkpte(pfn_pte(virt_to_pfn(kasan_early_shadow_page), PAGE_KERNEL));
>
>> +
>> + if (!early_radix_enabled())
>> + panic("KASAN requires radix!");
>> +
>> + 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);
>
> Same comment as above, use helpers ?
>
>> + 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);
>> +
>> + /*
>> + * clear_page relies on some cache info that hasn't been set up yet.
>> + * It ends up looping ~forever and blows up other data.
>> + * Use memset instead.
>> + */
>> + 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");
>> +}
>>
>
> Christophe

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