Hi Christophe,

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

quoted

--- 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

quoted

  
  		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);

quoted

  	}
  }
  

@@ -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 ?

quoted

+			      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.

quoted

+		DBG("reserving %llx -> %llx for KASAN",
+		    kasan_shadow_start, top_phys_addr);
+		memblock_reserve(kasan_shadow_start,
+				 top_phys_addr - kasan_shadow_start);

Same ?

quoted

+	}
  }
  
  #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 ?

quoted

+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));

quoted

+
+	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 ?

quoted

+	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