On Sat, Jan 09, 2021 at 06:32:49PM +0800, Lecopzer Chen wrote:

quoted

Linux support KAsan for VMALLOC since commit 3c5c3cfb9ef4da9
("kasan: support backing vmalloc space with real shadow memory")

Like how the MODULES_VADDR does now, just not to early populate
the VMALLOC_START between VMALLOC_END.
similarly, the kernel code mapping is now in the VMALLOC area and
should keep these area populated.

Signed-off-by: Lecopzer Chen <redacted>
---
 arch/arm64/mm/kasan_init.c | 23 ++++++++++++++++++-----
 1 file changed, 18 insertions(+), 5 deletions(-)

diff --git a/arch/arm64/mm/kasan_init.c b/arch/arm64/mm/kasan_init.c
index d8e66c78440e..39b218a64279 100644
--- a/arch/arm64/mm/kasan_init.c
+++ b/arch/arm64/mm/kasan_init.c

@@ -214,6 +214,7 @@ static void __init kasan_init_shadow(void)
 {
 	u64 kimg_shadow_start, kimg_shadow_end;
 	u64 mod_shadow_start, mod_shadow_end;
+	u64 vmalloc_shadow_start, vmalloc_shadow_end;
 	phys_addr_t pa_start, pa_end;
 	u64 i;
 

@@ -223,6 +224,9 @@ static void __init kasan_init_shadow(void)
 	mod_shadow_start = (u64)kasan_mem_to_shadow((void *)MODULES_VADDR);
 	mod_shadow_end = (u64)kasan_mem_to_shadow((void *)MODULES_END);
 
+	vmalloc_shadow_start = (u64)kasan_mem_to_shadow((void *)VMALLOC_START);
+	vmalloc_shadow_end = (u64)kasan_mem_to_shadow((void *)VMALLOC_END);
+
 	/*
 	 * We are going to perform proper setup of shadow memory.
 	 * At first we should unmap early shadow (clear_pgds() call below).

@@ -241,12 +245,21 @@ static void __init kasan_init_shadow(void)
 
 	kasan_populate_early_shadow(kasan_mem_to_shadow((void *)PAGE_END),
 				   (void *)mod_shadow_start);
-	kasan_populate_early_shadow((void *)kimg_shadow_end,
-				   (void *)KASAN_SHADOW_END);
+	if (IS_ENABLED(CONFIG_KASAN_VMALLOC)) {

Do we really need yet another CONFIG option for KASAN? What's the use-case
for *not* enabling this if you're already enabling one of the KASAN
backends?

As I know, KASAN_VMALLOC now only supports KASAN_GENERIC and also
KASAN_VMALLOC uses more memory to map real shadow memory (1/8 of vmalloc va).

There should be someone can enable KASAN_GENERIC but can't use VMALLOC
due to memory issue.
 

quoted

+		kasan_populate_early_shadow((void *)vmalloc_shadow_end,
+					    (void *)KASAN_SHADOW_END);
+		if (vmalloc_shadow_start > mod_shadow_end)

To echo Ard's concern: when is the above 'if' condition true?

After reviewing this code,
since VMALLOC_STAR is a compiler defined macro of MODULES_END,
this if-condition will never be true.

I also test it with removing this and works fine.

I'll remove this in the next version patch,
thanks a lot for pointing out this.

BRs,
Lecopzer

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