riscv: Fix kernel stack size when KASAN is enabled

We use Kconfig to select the kernel stack size, doubling the default
size if KASAN is enabled.

But that actually only works if KASAN is selected from the beginning,
meaning that if KASAN config is added later (for example using
menuconfig), CONFIG_THREAD_SIZE_ORDER won't be updated, keeping the
default size, which is not enough for KASAN as reported in [1].

So fix this by moving the logic to compute the right kernel stack into a
header.

Fixes: a7555f6b62e7 ("riscv: stack: Add config of thread stack size")
Reported-by: syzbot+ba9eac24453387a9d502@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/all/000000000000eb301906222aadc2@google.com/ [1]
Cc: stable@vger.kernel.org
Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Link: https://lore.kernel.org/r/20240917150328.59831-1-alexghiti@rivosinc.com
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>

diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index 22dc5ea..6254594 100644 (file)
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -777,8 +777,7 @@ config IRQ_STACKS
 config THREAD_SIZE_ORDER
        int "Kernel stack size (in power-of-two numbers of page size)" if VMAP_STACK && EXPERT
        range 0 4
-       default 1 if 32BIT && !KASAN
-       default 3 if 64BIT && KASAN
+       default 1 if 32BIT
        default 2
        help
          Specify the Pages of thread stack size (from 4KB to 64KB), which also

diff --git a/arch/riscv/include/asm/thread_info.h b/arch/riscv/include/asm/thread_info.h
index ebe52f9..9c10fb1 100644 (file)
--- a/arch/riscv/include/asm/thread_info.h
+++ b/arch/riscv/include/asm/thread_info.h
@@ -13,7 +13,12 @@
 #include <linux/sizes.h>
 
 /* thread information allocation */
-#define THREAD_SIZE_ORDER      CONFIG_THREAD_SIZE_ORDER
+#ifdef CONFIG_KASAN
+#define KASAN_STACK_ORDER      1
+#else
+#define KASAN_STACK_ORDER      0
+#endif
+#define THREAD_SIZE_ORDER      (CONFIG_THREAD_SIZE_ORDER + KASAN_STACK_ORDER)
 #define THREAD_SIZE            (PAGE_SIZE << THREAD_SIZE_ORDER)
 
 /*