Re: [PATCH] x86/acpi: fix potential NULL deref in acpi_wakeup_cpu()

[Kirill A. Shutemov]

On Tue, Apr 15, 2025 at 03:39:24PM +0200, Rafael J. Wysocki wrote:
> On Fri, Apr 11, 2025 at 9:48 PM Chenyuan Yang <chenyuan0y@xxxxxxxxx> wrote:
> >
> > The result of memremap() may be NULL on failure, leading to a NULL
> > dereference. Add explicit checks after memremap() call: if the
> > MADT mailbox fails to map, return immediately.
> >
> > This is similar to the commit 966d47e1f27c
> > ("efi: fix potential NULL deref in efi_mem_reserve_persistent").
> >
> > This is found by our static analysis tool KNighter.
> >
> > Signed-off-by: Chenyuan Yang <chenyuan0y@xxxxxxxxx>
> > Fixes: 2b5e22afae07 ("x86/acpi: Extract ACPI MADT wakeup code into a separate file")
> 
> Well, it's good to add the author of the commit you're trying to fix
> to the CC list.
> 
> Kirill, what do you think about this?

Looks reasonable to me.

We fail to remap a single page. It is likely to be fatally broken system
if we get there. But okay, let's handle it.

Maybe use pr_err_once(). No need to spam an error for every CPU.

> > ---
> >  arch/x86/kernel/acpi/madt_wakeup.c | 4 ++++
> >  1 file changed, 4 insertions(+)
> >
> > diff --git a/arch/x86/kernel/acpi/madt_wakeup.c b/arch/x86/kernel/acpi/madt_wakeup.c
> > index f36f28405dcc..b386ec4b87c2 100644
> > --- a/arch/x86/kernel/acpi/madt_wakeup.c
> > +++ b/arch/x86/kernel/acpi/madt_wakeup.c
> > @@ -143,6 +143,10 @@ static int acpi_wakeup_cpu(u32 apicid, unsigned long start_ip)
> >                 acpi_mp_wake_mailbox = memremap(acpi_mp_wake_mailbox_paddr,
> >                                                 sizeof(*acpi_mp_wake_mailbox),
> >                                                 MEMREMAP_WB);
> > +               if (!acpi_mp_wake_mailbox) {
> > +                       pr_err("Failed to remap MADT mailbox\n");
> > +                       return -ENOMEM;
> > +               }
> >         }
> >
> >         /*
> > --
> > 2.34.1
> >

-- 
  Kiryl Shutsemau / Kirill A. Shutemov