This fixes a problem, where booting Linux using distro boot will sometimes lead to an invalid instruction exception on the main hart. The secondary harts are not affected and boot Linux successfully. The root cause of this problem is a stack overflow on the main hart.

With distro boot, the current default stack size of 8KiB on RISC-V is not sufficient and will cause a stack overflow. The stacks are allocated sequentially. In the case of a stack overflow the stack of the main hart can reach into that of another hart and be corrupted.

The stack overflow previously did not cause any problems, because only stack frames, which are not used anymore since the hart enters Linux, were corrupted. Starting with GCC 9, the stack usage has decreased. Now, only the most recent stack frame overflows into the stack of a secondary hart and is corrupted. The illegal instruction exception is caused by the secondary hart overwriting the return address in the stack frame of the main hart with an address that does not include valid code.

Increase the default stack size of each hart to 16KiB to avoid this problem.

Reported-by: Aurelien Jarno aurelien@aurel32.net Signed-off-by: Lukas Auer lukas.auer@aisec.fraunhofer.de Tested-by: David Abdurachmanov david.abdurachmanov@sifive.com Tested-by: Aurelien Jarno aurelien@aurel32.net ---

arch/riscv/Kconfig | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig index 01975d7c60..85e15ebffa 100644 --- a/arch/riscv/Kconfig +++ b/arch/riscv/Kconfig @@ -224,7 +224,7 @@ config XIP

config STACK_SIZE_SHIFT int - default 13 + default 14

config SPL_LDSCRIPT default "arch/riscv/cpu/u-boot-spl.lds"