[PATCH] arm64: kasan: avoid pfn_to_nid() before page array is initialized

[Mark Rutland]

In arm64's kasan_init(), we use pfn_to_nid() to find the NUMA node a
span of memory is in, hoping to allocate shadow from the same NUMA node.
However, at this point, the page array has not been initialized, and
thus this is bogus.

Since commit:

  f165b378bbdf6c8a ("mm: uninitialized struct page poisoning sanity")

... accessing fields of the page array results in a boot time Oops(),
highlighting this problem:

[    0.000000] Unable to handle kernel paging request at virtual address dfff200000000000
[    0.000000] Mem abort info:
[    0.000000]   ESR = 0x96000004
[    0.000000]   Exception class = DABT (current EL), IL = 32 bits
[    0.000000]   SET = 0, FnV = 0
[    0.000000]   EA = 0, S1PTW = 0
[    0.000000] Data abort info:
[    0.000000]   ISV = 0, ISS = 0x00000004
[    0.000000]   CM = 0, WnR = 0
[    0.000000] [dfff200000000000] address between user and kernel address ranges
[    0.000000] Internal error: Oops: 96000004 [#1] PREEMPT SMP
[    0.000000] Modules linked in:
[    0.000000] CPU: 0 PID: 0 Comm: swapper Not tainted 4.16.0-07317-gf165b378bbdf #42
[    0.000000] Hardware name: ARM Juno development board (r1) (DT)
[    0.000000] pstate: 80000085 (Nzcv daIf -PAN -UAO)
[    0.000000] pc : __asan_load8+0x8c/0xa8
[    0.000000] lr : __dump_page+0x3c/0x3b8
[    0.000000] sp : ffff2000099b7ca0
[    0.000000] x29: ffff2000099b7ca0 x28: ffff20000a1762c0
[    0.000000] x27: ffff7e0000000000 x26: ffff2000099dd000
[    0.000000] x25: ffff200009a3f960 x24: ffff200008f9c38c
[    0.000000] x23: ffff20000a9d3000 x22: ffff200009735430
[    0.000000] x21: fffffffffffffffe x20: ffff7e0001e50420
[    0.000000] x19: ffff7e0001e50400 x18: 0000000000001840
[    0.000000] x17: ffffffffffff8270 x16: 0000000000001840
[    0.000000] x15: 0000000000001920 x14: 0000000000000004
[    0.000000] x13: 0000000000000000 x12: 0000000000000800
[    0.000000] x11: 1ffff0012d0f89ff x10: ffff10012d0f89ff
[    0.000000] x9 : 0000000000000000 x8 : ffff8009687c5000
[    0.000000] x7 : 0000000000000000 x6 : ffff10000f282000
[    0.000000] x5 : 0000000000000040 x4 : fffffffffffffffe
[    0.000000] x3 : 0000000000000000 x2 : dfff200000000000
[    0.000000] x1 : 0000000000000005 x0 : 0000000000000000
[    0.000000] Process swapper (pid: 0, stack limit = 0x        (ptrval))
[    0.000000] Call trace:
[    0.000000]  __asan_load8+0x8c/0xa8
[    0.000000]  __dump_page+0x3c/0x3b8
[    0.000000]  dump_page+0xc/0x18
[    0.000000]  kasan_init+0x2e8/0x5a8
[    0.000000]  setup_arch+0x294/0x71c
[    0.000000]  start_kernel+0xdc/0x500
[    0.000000] Code: aa0403e0 9400063c 17ffffee d343fc00 (38e26800)
[    0.000000] ---[ end trace 67064f0e9c0cc338 ]---
[    0.000000] Kernel panic - not syncing: Attempted to kill the idle task!
[    0.000000] ---[ end Kernel panic - not syncing: Attempted to kill the idle task! ]---

Let's fix this by using early_pfn_to_nid(), as other architectures do in
their kasan init code. Note that early_pfn_to_nid acquires the nid from
the memblock array, which we iterate over in kasan_init(), so this
should be fine.

Signed-off-by: Mark Rutland <mark.rutland at arm.com>
Fixes: 39d114ddc6822302 ("arm64: add KASAN support")
Cc: Catalin Marinas <catalin.marinas at arm.com>
Cc: Will Deacon <will.deacon at arm.com>
---
 arch/arm64/mm/kasan_init.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

Catalin, are you happy to pick this up as a fix for v4.17-rc2?

I spotted this while preparing a v4.17-rc1 Image for fuzzing...

Thanks,
Mark.

diff --git a/arch/arm64/mm/kasan_init.c b/arch/arm64/mm/kasan_init.c
index dabfc1ecda3d..12145874c02b 100644
--- a/arch/arm64/mm/kasan_init.c
+++ b/arch/arm64/mm/kasan_init.c
@@ -204,7 +204,7 @@ void __init kasan_init(void)
 	clear_pgds(KASAN_SHADOW_START, KASAN_SHADOW_END);
 
 	kasan_map_populate(kimg_shadow_start, kimg_shadow_end,
-			   pfn_to_nid(virt_to_pfn(lm_alias(_text))));
+			   early_pfn_to_nid(virt_to_pfn(lm_alias(_text))));
 
 	kasan_populate_zero_shadow((void *)KASAN_SHADOW_START,
 				   (void *)mod_shadow_start);
@@ -224,7 +224,7 @@ void __init kasan_init(void)
 
 		kasan_map_populate((unsigned long)kasan_mem_to_shadow(start),
 				   (unsigned long)kasan_mem_to_shadow(end),
-				   pfn_to_nid(virt_to_pfn(start)));
+				   early_pfn_to_nid(virt_to_pfn(start)));
 	}
 
 	/*
-- 
2.11.0