[PATCH] riscv: mm: Add KASAN shadow mapping to flush_cache_vmap()

[Ali Tariq <alitariq45892@gmail.com>]

flush_cache_vmap() sets a per-CPU flag, and a kernel page fault
that finds the flag set gets an sfence.vma and a retry.
flush_cache_vmap() only sets the flag for vmalloc, module and vmemmap
ranges. kasan_populate_vmalloc() maps new shadow pages and calls
flush_cache_vmap() on the shadow range, so no flag gets set.
For vmap()-style areas, kasan_unpoison_vmalloc() writes
the new shadow right away. If the CPU hasn’t seen the new entry yet,
the store faults, and since there is no flag set, the kernel crashes.

[    0.675216] Unable to handle kernel paging request at virtual address fffffff7c009a000
Current swapper/0 pgtable: 4K pagesize, 39-bit VAs, pgdp=0x0000000004504000
[fffffff7c009a000] pgd=000000009ff6e001, p4d=000000009ff6e001, pud=000000009ff6e001, pmd=00000000400e7401, pte=00000000403cb0e7
status: 0000000200000120 badaddr: fffffff7c009a000 cause: 000000000000000f
__memset+0x60/0xfe
kasan_unpoison+0x26/0x4e
__kasan_unpoison_vmalloc+0x20/0x2e
__get_vm_area_node+0x1c6/0x276
get_vm_area_caller+0x52/0x84
vmap+0xf0/0x264
dma_common_contiguous_remap+0xa0/0xd0
atomic_pool_expand+0xb6/0x310
__dma_atomic_pool_init.isra.0+0xf6/0x1c0
dma_atomic_pool_init+0xf6/0x1aa
do_one_initcall+0x134/0x928
kernel_init_freeable+0x532/0x60a
kernel_init+0x28/0x162
ret_from_fork_kernel+0x82/0x94c
ret_from_fork_kernel_asm+0x16/0x18

The PTE is valid, so the mapping was in place when the CPU faulted.

Tested on Orange Pi RV2: without this patch 2 of 30 boots crashed,
with it 50 of 50 booted.

Add the KASAN shadow region to the ranges for which flush_cache_vmap()
calls mark_new_valid_map(), as commit 4edd70ee6a7d ("mm/sparse-vmemmap:
flush_cache_vmap() after hotplugging vmemmap") did for vmemmap.

Fixes: 503638e0babf ("riscv: Stop emitting preventive sfence.vma for new vmalloc mappings")
Signed-off-by: Ali Tariq <alitariq45892@gmail.com>
---
Crash Log: https://kernelci.cloud-v.co/scheduler/job/541
---
 arch/riscv/include/asm/cacheflush.h | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/arch/riscv/include/asm/cacheflush.h b/arch/riscv/include/asm/cacheflush.h
index c2b0a2928f06..c95b2f6007fd 100644
--- a/arch/riscv/include/asm/cacheflush.h
+++ b/arch/riscv/include/asm/cacheflush.h
@@ -8,6 +8,8 @@
 
 #include <linux/mm.h>
 
+#include <asm/kasan.h>
+
 static inline void local_flush_icache_all(void)
 {
 	asm volatile ("fence.i" ::: "memory");
@@ -57,7 +59,9 @@ static inline void mark_new_valid_map(void)
 static inline void flush_cache_vmap(unsigned long start, unsigned long end)
 {
 	if (is_vmalloc_or_module_addr((void *)start) ||
-	    (start >= VMEMMAP_START && end <= VMEMMAP_END))
+	    (start >= VMEMMAP_START && end <= VMEMMAP_END) ||
+	    (IS_ENABLED(CONFIG_KASAN) &&
+	     start >= KASAN_SHADOW_START && end <= KASAN_SHADOW_END))
 		mark_new_valid_map();
 }
 #define flush_cache_vmap_early(start, end)	local_flush_tlb_kernel_range(start, end)
-- 
2.34.1