From 5b1cfe3a0ba74c1f2b83b607712a217b9f9463a2 Mon Sep 17 00:00:00 2001 From: Will Deacon Date: Tue, 27 Aug 2019 14:36:38 +0100 Subject: [PATCH] arm64: smp: Don't enter kernel with NULL stack pointer or task struct Although SMP bringup is inherently racy, we can significantly reduce the window during which secondary CPUs can unexpectedly enter the kernel by sanity checking the 'stack' and 'task' fields of the 'secondary_data' structure. If the booting CPU gave up waiting for us, then they will have been cleared to NULL and we should spin in a WFE; WFI loop instead. Reviewed-by: Mark Rutland Signed-off-by: Will Deacon --- arch/arm64/kernel/head.S | 8 ++++++++ arch/arm64/kernel/smp.c | 1 + 2 files changed, 9 insertions(+) diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S index 2cdacd1..0baadf3 100644 --- a/arch/arm64/kernel/head.S +++ b/arch/arm64/kernel/head.S @@ -724,14 +724,22 @@ __secondary_switched: adr_l x0, secondary_data ldr x1, [x0, #CPU_BOOT_STACK] // get secondary_data.stack + cbz x1, __secondary_too_slow mov sp, x1 ldr x2, [x0, #CPU_BOOT_TASK] + cbz x2, __secondary_too_slow msr sp_el0, x2 mov x29, #0 mov x30, #0 b secondary_start_kernel ENDPROC(__secondary_switched) +__secondary_too_slow: + wfe + wfi + b __secondary_too_slow +ENDPROC(__secondary_too_slow) + /* * The booting CPU updates the failed status @__early_cpu_boot_status, * with MMU turned off. diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c index 63c7a76..1f8aeb7 100644 --- a/arch/arm64/kernel/smp.c +++ b/arch/arm64/kernel/smp.c @@ -136,6 +136,7 @@ int __cpu_up(unsigned int cpu, struct task_struct *idle) secondary_data.task = NULL; secondary_data.stack = NULL; + __flush_dcache_area(&secondary_data, sizeof(secondary_data)); status = READ_ONCE(secondary_data.status); if (ret && status) { -- 2.7.4