powerpc/kasan: Force thread size increase with KASAN

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@mailbox.org>
Reported-by: Christophe Leroy <christophe.leroy@csgroup.eu>
[mpe: Use MIN_THREAD_SHIFT as suggested by Christophe]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220601143114.133524-1-mpe@ellerman.id.au

diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 54dbbb1..b1760d6 100644 (file)
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -790,7 +790,6 @@ 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 125328d..af58f1e 100644 (file)
--- 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)