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 <j...@jms.id.au>
Signed-off-by: Michael Ellerman <m...@ellerman.id.au>
Reviewed-by: Christophe Leroy <christophe.le...@c-s.fr>
---
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 */
