From: Greentime Hu <greentime.hu@xxxxxxxxxx> Early function calls, such as setup_vm(), relocate_enable_mmu(), soc_early_init() etc, are free to operate on stack. However, PT_SIZE_ON_STACK bytes at the head of the kernel stack are purposedly reserved for the placement of per-task register context pointed by task_pt_regs(p). Those functions may corrupt task_pt_regs if we overlap the $sp with it. In fact, we had accidentally corrupted sstatus.VS in some tests, treating the kernel to save V context before V was actually allocated, resulting in a kernel panic. Thus, we should skip PT_SIZE_ON_STACK for $sp before making C function calls from the top-level assembly. Co-developed-by: ShihPo Hung <shihpo.hung@xxxxxxxxxx> Signed-off-by: ShihPo Hung <shihpo.hung@xxxxxxxxxx> Co-developed-by: Vincent Chen <vincent.chen@xxxxxxxxxx> Signed-off-by: Vincent Chen <vincent.chen@xxxxxxxxxx> Signed-off-by: Greentime Hu <greentime.hu@xxxxxxxxxx> Signed-off-by: Andy Chiu <andy.chiu@xxxxxxxxxx> Reviewed-by: Conor Dooley <conor.dooley@xxxxxxxxxxxxx> Reviewed-by: Heiko Stuebner <heiko.stuebner@xxxxxxxx> Tested-by: Heiko Stuebner <heiko.stuebner@xxxxxxxx> --- arch/riscv/kernel/head.S | 2 ++ 1 file changed, 2 insertions(+) diff --git a/arch/riscv/kernel/head.S b/arch/riscv/kernel/head.S index e16bb2185d55..11c3b94c4534 100644 --- a/arch/riscv/kernel/head.S +++ b/arch/riscv/kernel/head.S @@ -301,6 +301,7 @@ clear_bss_done: la tp, init_task la sp, init_thread_union + THREAD_SIZE XIP_FIXUP_OFFSET sp + addi sp, sp, -PT_SIZE_ON_STACK #ifdef CONFIG_BUILTIN_DTB la a0, __dtb_start XIP_FIXUP_OFFSET a0 @@ -318,6 +319,7 @@ clear_bss_done: /* Restore C environment */ la tp, init_task la sp, init_thread_union + THREAD_SIZE + addi sp, sp, -PT_SIZE_ON_STACK #ifdef CONFIG_KASAN call kasan_early_init -- 2.17.1
