Re: [PATCHv2 5/5] efi/runtime-wrappers: detect FW irq flag corruption

Ard Biesheuvel
2016-04-21T17:05:35Z

On 21 April 2016 at 13:35, Mark Rutland <mark.rutland@arm.com> wrote:
> The UEFI spec allows runtime services to be called with interrupts
> masked or unmasked, and if a runtime service function needs to mask
> interrupts, it must restore the mask to its original state before
> returning (i.e. from the PoV of the OS, this does not change across a
> call). Firmware should never unmask exceptions, as these may then be
> taken by the OS unexpectedly.
>
> Unfortunately, some firmware has been seen to unmask IRQs (and
> potentially other maskable exceptions) across runtime services calls,
> leaving irq flags corrupted after returning from a runtime services
> function call. This may be detected by the IRQ tracing code, but often
> goes unnoticed, leaving a potentially disastrous bug hidden.
>
> This patch detects when the irq flags are corrupted by an EFI runtime
> services call, logging the call and specific corruption to the console.
> While restoring the expected value of the flags is insufficient to avoid
> problems, we do so to avoid redundant warnings from elsewhere (e.g. IRQ
> tracing).
>
> Signed-off-by: Mark Rutland <mark.rutland@arm.com>
> Cc: Matt Fleming <matt@codeblueprint.co.uk>
> Cc: linux-efi@vger.kernel.org
> Cc: linux-kernel@vger.kernel.org
> ---
> drivers/firmware/efi/runtime-wrappers.c | 22 ++++++++++++++++++++++
> 1 file changed, 22 insertions(+)
>
> diff --git a/drivers/firmware/efi/runtime-wrappers.c b/drivers/firmware/efi/runtime-wrappers.c
> index 1b9fa54..aeb65f2 100644
> --- a/drivers/firmware/efi/runtime-wrappers.c
> +++ b/drivers/firmware/efi/runtime-wrappers.c
> @@ -16,8 +16,10 @@
>
> #include <linux/bug.h>
> #include <linux/efi.h>
> +#include <linux/irqflags.h>
> #include <linux/mutex.h>
> #include <linux/spinlock.h>
> +#include <linux/stringify.h>
> #include <asm/efi.h>
>
>
> @@ -25,8 +27,11 @@
> #define efi_call_virt(f, args...) \
> ({ \
> efi_status_t __s; \
> + unsigned long flags; \
> arch_efi_call_virt_setup(); \
> + local_save_flags(flags); \
> __s = arch_efi_call_virt(f, args); \
> + efi_call_virt_check_flags(flags, __stringify(f)); \
> arch_efi_call_virt_teardown(); \
> __s; \
> })
> @@ -35,12 +40,29 @@
> #ifndef __efi_call_virt
> #define __efi_call_virt(f, args...) \
> ({ \
> + unsigned long flags; \
> arch_efi_call_virt_setup(); \
> + local_irq_save(flags); \

We shouldn't disable interrupts here. I assume this is a typo, and you
intended to use local_save_flags() as above?

> arch_efi_call_virt(f, args); \
> + efi_call_virt_check_flags(flags, __stringify(f)); \
> arch_efi_call_virt_teardown(); \
> })
> #endif
>
> +static void efi_call_virt_check_flags(unsigned long flags, const char *call)
> +{
> + unsigned long cur_flags;
> +
> + local_save_flags(cur_flags);
> + if (!WARN_ON_ONCE(cur_flags != flags))
> + return;
> +
> + add_taint(TAINT_FIRMWARE_WORKAROUND, LOCKDEP_NOW_UNRELIABLE);
> + pr_err_ratelimited(FW_BUG "IRQ flags corrupted (0x%08lx=>0x%08lx) by EFI %s\n",
> + flags, cur_flags, call);
> + local_irq_restore(flags);
> +}
> +
> /*
> * According to section 7.1 of the UEFI spec, Runtime Services are not fully
> * reentrant, and there are particular combinations of calls that need to be

Other than that, this series looks fine to me.

With the above fixed:

For the series (except the x86 patch)

Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>