linux-kernel - [PATCH] powerpc/32: disable KASAN with pages bigger than 16k

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Date:   Thu, 28 May 2020 10:17:04 +0000 (UTC)
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>
Cc:     linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: [PATCH] powerpc/32: disable KASAN with pages bigger than 16k

Mapping of early shadow area is implemented by using a single static
page table having all entries pointing to the same early shadow page.
The shadow area must therefore occupy full PGD entries.

The shadow area has a size of 128Mbytes starting at 0xf8000000.
With 4k pages, a PGD entry is 4Mbytes
With 16k pages, a PGD entry is 64Mbytes
With 64k pages, a PGD entry is 256Mbytes which is too big.

Until we rework the early shadow mapping, disable KASAN when the
page size is too big.

Reported-by: kbuild test robot <lkp@...el.com>
Fixes: 2edb16efc899 ("powerpc/32: Add KASAN support")
Cc: stable@...r.kernel.org
Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
---
 arch/powerpc/Kconfig | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 1dfa59126fcf..066b36bf9efa 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -169,8 +169,8 @@ config PPC
 	select HAVE_ARCH_AUDITSYSCALL
 	select HAVE_ARCH_HUGE_VMAP		if PPC_BOOK3S_64 && PPC_RADIX_MMU
 	select HAVE_ARCH_JUMP_LABEL
-	select HAVE_ARCH_KASAN			if PPC32
-	select HAVE_ARCH_KASAN_VMALLOC		if PPC32
+	select HAVE_ARCH_KASAN			if PPC32 && PPC_PAGE_SHIFT <= 14
+	select HAVE_ARCH_KASAN_VMALLOC		if PPC32 && PPC_PAGE_SHIFT <= 14
 	select HAVE_ARCH_KGDB
 	select HAVE_ARCH_MMAP_RND_BITS
 	select HAVE_ARCH_MMAP_RND_COMPAT_BITS	if COMPAT
-- 
2.25.0