linux-kernel - Re: [PATCH] x86/acpi: fix potential NULL deref in acpi_wakeup

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Message-ID: <CAJZ5v0g9YZLct_OkQsNDeh3HUv9YccvvT18JJd8Hu9JpQ0ksRw@mail.gmail.com>
Date: Fri, 16 May 2025 16:07:30 +0200
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Chenyuan Yang <chenyuan0y@...il.com>
Cc: rafael@...nel.org, lenb@...nel.org, tglx@...utronix.de, mingo@...hat.com, 
	bp@...en8.de, dave.hansen@...ux.intel.com, x86@...nel.org, hpa@...or.com, 
	bhe@...hat.com, kai.huang@...el.com, 
	sathyanarayanan.kuppuswamy@...ux.intel.com, linux-acpi@...r.kernel.org, 
	linux-kernel@...r.kernel.org, 
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: Re: [PATCH] x86/acpi: fix potential NULL deref in acpi_wakeup_cpu()

On Fri, Apr 11, 2025 at 9:48 PM Chenyuan Yang <chenyuan0y@...il.com> 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 mailbox is called Multiprocessor Wakeup Mailbox in the
specification, so please follow the established terminology.

> 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@...il.com>
> Fixes: 2b5e22afae07 ("x86/acpi: Extract ACPI MADT wakeup code into a separate file")
> ---
>  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");

Please follow Kirill's advice on using pr_err_once() here and use the
proper terminology in the message (also this is mapping, not
remapping, even though memremap() is used).

> +                       return -ENOMEM;
> +               }
>         }
>
>         /*
> --

Thanks!