[PATCH 5.15 135/247] powerpc/kasan: Force thread size increase with KASAN

[Greg Kroah-Hartman]

From: Michael Ellerman <mpe@xxxxxxxxxxxxxx>

[ Upstream commit 3e8635fb2e072672cbc650989ffedf8300ad67fb ]

KASAN causes increased stack usage, which can lead to stack overflows.

The logic in Kconfig to suggest a larger default doesn't work if a user
has CONFIG_EXPERT enabled and has an existing .config with a smaller
value.

Follow the lead of x86 and arm64, and force the thread size to be
increased when KASAN is enabled.

That also has the effect of enlarging the stack for 64-bit KASAN builds,
which is also desirable.

Fixes: edbadaf06710 ("powerpc/kasan: Fix stack overflow by increasing THREAD_SHIFT")
Reported-by: Erhard Furtner <erhard_f@xxxxxxxxxxx>
Reported-by: Christophe Leroy <christophe.leroy@xxxxxxxxxx>
[mpe: Use MIN_THREAD_SHIFT as suggested by Christophe]
Signed-off-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20220601143114.133524-1-mpe@xxxxxxxxxxxxxx
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 arch/powerpc/Kconfig                   |  1 -
 arch/powerpc/include/asm/thread_info.h | 10 ++++++++--
 2 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 6b9f523882c5..3bd3a3f16648 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -768,7 +768,6 @@ config THREAD_SHIFT
 	range 13 15
 	default "15" if PPC_256K_PAGES
 	default "14" if PPC64
-	default "14" if KASAN
 	default "13"
 	help
 	  Used to define the stack size. The default is almost always what you
diff --git a/arch/powerpc/include/asm/thread_info.h b/arch/powerpc/include/asm/thread_info.h
index 2a4ea0e213a9..87013ac2a640 100644
--- a/arch/powerpc/include/asm/thread_info.h
+++ b/arch/powerpc/include/asm/thread_info.h
@@ -14,10 +14,16 @@
 
 #ifdef __KERNEL__
 
-#if defined(CONFIG_VMAP_STACK) && CONFIG_THREAD_SHIFT < PAGE_SHIFT
+#ifdef CONFIG_KASAN
+#define MIN_THREAD_SHIFT	(CONFIG_THREAD_SHIFT + 1)
+#else
+#define MIN_THREAD_SHIFT	CONFIG_THREAD_SHIFT
+#endif
+
+#if defined(CONFIG_VMAP_STACK) && MIN_THREAD_SHIFT < PAGE_SHIFT
 #define THREAD_SHIFT		PAGE_SHIFT
 #else
-#define THREAD_SHIFT		CONFIG_THREAD_SHIFT
+#define THREAD_SHIFT		MIN_THREAD_SHIFT
 #endif
 
 #define THREAD_SIZE		(1 << THREAD_SHIFT)
-- 
2.35.1