[ Upstream commit 7dbcf2b0b770eeb803a416ee8dcbef78e6389d40 ]
Commit
37fe6a42b343 ("x86: Check stack overflow in detail")
added a broad check for the full exception stack area, i.e. it considers the full exception stack area as valid.
That's wrong in two aspects:
1) It does not check the individual areas one by one
2) #DF, NMI and #MCE are not enabling interrupts which means that a regular device interrupt cannot happen in their context. In fact if a device interrupt hits one of those IST stacks that's a bug because some code path enabled interrupts while handling the exception.
Limit the check to the #DB stack and consider all other IST stacks as 'overflow' or invalid.
Signed-off-by: Thomas Gleixner tglx@linutronix.de Signed-off-by: Borislav Petkov bp@suse.de Cc: Andy Lutomirski luto@kernel.org Cc: "H. Peter Anvin" hpa@zytor.com Cc: Ingo Molnar mingo@redhat.com Cc: Josh Poimboeuf jpoimboe@redhat.com Cc: Mitsuo Hayasaka mitsuo.hayasaka.hu@hitachi.com Cc: Nicolai Stange nstange@suse.de Cc: Sean Christopherson sean.j.christopherson@intel.com Cc: x86-ml x86@kernel.org Link: https://lkml.kernel.org/r/20190414160143.682135110@linutronix.de Signed-off-by: Sasha Levin sashal@kernel.org --- arch/x86/kernel/irq_64.c | 19 ++++++++++++++----- 1 file changed, 14 insertions(+), 5 deletions(-)
diff --git a/arch/x86/kernel/irq_64.c b/arch/x86/kernel/irq_64.c index bcd1b82c86e81..005e9a77a664e 100644 --- a/arch/x86/kernel/irq_64.c +++ b/arch/x86/kernel/irq_64.c @@ -25,9 +25,18 @@ int sysctl_panic_on_stackoverflow; /* * Probabilistic stack overflow check: * - * Only check the stack in process context, because everything else - * runs on the big interrupt stacks. Checking reliably is too expensive, - * so we just check from interrupts. + * Regular device interrupts can enter on the following stacks: + * + * - User stack + * + * - Kernel task stack + * + * - Interrupt stack if a device driver reenables interrupts + * which should only happen in really old drivers. + * + * - Debug IST stack + * + * All other contexts are invalid. */ static inline void stack_overflow_check(struct pt_regs *regs) { @@ -52,8 +61,8 @@ static inline void stack_overflow_check(struct pt_regs *regs) return;
oist = this_cpu_ptr(&orig_ist); - estack_top = (u64)oist->ist[0] - EXCEPTION_STKSZ + STACK_TOP_MARGIN; - estack_bottom = (u64)oist->ist[N_EXCEPTION_STACKS - 1]; + estack_bottom = (u64)oist->ist[DEBUG_STACK]; + estack_top = estack_bottom - DEBUG_STKSZ + STACK_TOP_MARGIN; if (regs->sp >= estack_top && regs->sp <= estack_bottom) return;