Re: [PATCH] powerpc: Fix stack protector crashes on CPU hotplug
From: Christophe LEROY <hidden>
Date: 2018-10-19 06:22:50
Le 19/10/2018 à 07:59, Michael Ellerman a écrit :
Recently in commit 7241d26e8175 ("powerpc/64: properly initialise
the stackprotector canary on SMP.") we fixed a crash with stack
protector on SMP by initialising the stack canary in
cpu_idle_thread_init().
But this can also causes crashes, when a CPU comes back online after
being offline:
Kernel panic - not syncing: stack-protector: Kernel stack is corrupted in: pnv_smp_cpu_kill_self+0x2a0/0x2b0
CPU: 1 PID: 0 Comm: swapper/1 Not tainted 4.19.0-rc3-gcc-7.3.1-00168-g4ffe713b7587 #94
Call Trace:
dump_stack+0xb0/0xf4 (unreliable)
panic+0x144/0x328
__stack_chk_fail+0x2c/0x30
pnv_smp_cpu_kill_self+0x2a0/0x2b0
cpu_die+0x48/0x70
arch_cpu_idle_dead+0x20/0x40
do_idle+0x274/0x390
cpu_startup_entry+0x38/0x50
start_secondary+0x5e4/0x600
start_secondary_prolog+0x10/0x14
Looking at the stack we see that the canary value in the stack frame
doesn't match the canary in the task/paca. That is because we have
reinitialised the task/paca value, but then the CPU coming online has
returned into a function using the old canary value. That causes the
comparison to fail.
Instead we can call boot_init_stack_canary() from start_secondary()
which never returns. This is essentially what the generic code does in
cpu_startup_entry() under #ifdef X86, we should make that non-x86
specific in a future patch.This shall not be done on arches that uses a global canary, so I think it has to be kept arch specific. Indeed I think x86 should move it to cpu_bringup_and_idle(). I'll propose them a patch for that. Christophe
Fixes: 7241d26e8175 ("powerpc/64: properly initialise the stackprotector canary on SMP.")
Reported-by: Joel Stanley <joel@jms.id.au>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>Reviewed-by: Christophe Leroy <redacted>
quoted hunk ↗ jump to hunk
--- arch/powerpc/kernel/smp.c | 10 +++------- 1 file changed, 3 insertions(+), 7 deletions(-)diff --git a/arch/powerpc/kernel/smp.c b/arch/powerpc/kernel/smp.c index 8e3a5da24d59..951c476faffc 100644 --- a/arch/powerpc/kernel/smp.c +++ b/arch/powerpc/kernel/smp.c@@ -61,6 +61,7 @@ #include <asm/asm-prototypes.h> #include <asm/cpu_has_feature.h> #include <asm/ftrace.h> +#include <asm/stackprotector.h> #ifdef DEBUG #include <asm/udbg.h>@@ -1014,16 +1015,9 @@ static void cpu_idle_thread_init(unsigned int cpu, struct task_struct *idle) { struct thread_info *ti = task_thread_info(idle); -#ifdef CONFIG_STACKPROTECTOR - idle->stack_canary = get_random_canary(); -#endif - #ifdef CONFIG_PPC64 paca_ptrs[cpu]->__current = idle; paca_ptrs[cpu]->kstack = (unsigned long)ti + THREAD_SIZE - STACK_FRAME_OVERHEAD; -#ifdef CONFIG_STACKPROTECTOR - paca_ptrs[cpu]->canary = idle->stack_canary; -#endif #endif ti->cpu = cpu; secondary_ti = current_set[cpu] = ti;@@ -1316,6 +1310,8 @@ void start_secondary(void *unused) notify_cpu_starting(cpu); set_cpu_online(cpu, true); + boot_init_stack_canary(); + local_irq_enable(); /* We can enable ftrace for secondary cpus now */