[PATCH v2 1/2] riscv: Do not re-populate shadow memory with kasan_populate_early_shadow

Alexandre Ghiti alexandre.ghiti at canonical.com
Thu Oct 28 21:59:26 PDT 2021

When calling this function, all the shadow memory is already populated
with kasan_early_shadow_pte which has PAGE_KERNEL protection.
kasan_populate_early_shadow write-protects the mapping of the range
of addresses passed in argument in zero_pte_populate, which actually
write-protects all the shadow memory mapping since kasan_early_shadow_pte
is used for all the shadow memory at this point. And then when using
memblock API to populate the shadow memory, the first write access to the
kernel stack triggers a trap. This becomes visible with the next commit
that contains a fix for asan-stack.

We already manually populate all the shadow memory in kasan_early_init
and we write-protect kasan_early_shadow_pte at the end of kasan_init
which makes the calls to kasan_populate_early_shadow superfluous so
we can remove them.

Signed-off-by: Alexandre Ghiti <alexandre.ghiti at canonical.com>
 arch/riscv/mm/kasan_init.c | 11 -----------
 1 file changed, 11 deletions(-)

diff --git a/arch/riscv/mm/kasan_init.c b/arch/riscv/mm/kasan_init.c
index d7189c8714a9..89a8376ce44e 100644
--- a/arch/riscv/mm/kasan_init.c
+++ b/arch/riscv/mm/kasan_init.c
@@ -172,21 +172,10 @@ void __init kasan_init(void)
 	phys_addr_t p_start, p_end;
 	u64 i;
-	/*
-	 * Populate all kernel virtual address space with kasan_early_shadow_page
-	 * except for the linear mapping and the modules/kernel/BPF mapping.
-	 */
-	kasan_populate_early_shadow((void *)KASAN_SHADOW_START,
-				    (void *)kasan_mem_to_shadow((void *)
-								VMEMMAP_END));
 			(void *)kasan_mem_to_shadow((void *)VMALLOC_START),
 			(void *)kasan_mem_to_shadow((void *)VMALLOC_END));
-	else
-		kasan_populate_early_shadow(
-			(void *)kasan_mem_to_shadow((void *)VMALLOC_START),
-			(void *)kasan_mem_to_shadow((void *)VMALLOC_END));
 	/* Populate the linear mapping */
 	for_each_mem_range(i, &p_start, &p_end) {

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