linux-kernel - Re: [PATCHv2 0/6] efi: detect erroneous firmware IRQ manipulation

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Date:	Mon, 25 Apr 2016 11:51:53 +0100
From:	Matt Fleming <matt@...eblueprint.co.uk>
To:	Mark Rutland <mark.rutland@....com>
Cc:	Ard Biesheuvel <ard.biesheuvel@...aro.org>,
	Laszlo Ersek <lersek@...hat.com>,
	"linux-efi@...r.kernel.org" <linux-efi@...r.kernel.org>,
	Catalin Marinas <catalin.marinas@....com>,
	"hpa@...or.com" <hpa@...or.com>,
	Leif Lindholm <leif.lindholm@...aro.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"mingo@...hat.com" <mingo@...hat.com>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	Will Deacon <will.deacon@....com>
Subject: Re: [PATCHv2 0/6] efi: detect erroneous firmware IRQ manipulation

On Mon, 25 Apr, at 11:40:09AM, Mark Rutland wrote:
> 
> It looks like irqs_disabled_flags() will do what you expect, and ignore
> everything but the interrupt flag.
> 
> However, for ARM that will ignore the other exceptions we've seen FW
> erroneously unmask (e.g. FIQ), which is unfortunate, as fiddling with
> those is just as disastrous.
 
Bah, right.

> Would you be happy with an arch_efi_call_check_flags(before, after),
> instead? That way we can make the flags we check arch-specific.

Could we just make the flag mask arch-specific instead of the call
since the rest of efi_call_virt_check_flags() is good?

Something like this (uncompiled, untested, half-baked),

---

diff --git a/drivers/firmware/efi/runtime-wrappers.c b/drivers/firmware/efi/runtime-wrappers.c
index c38b1cfc26e2..057d00bee7d6 100644
--- a/drivers/firmware/efi/runtime-wrappers.c
+++ b/drivers/firmware/efi/runtime-wrappers.c
@@ -25,9 +25,12 @@
 static void efi_call_virt_check_flags(unsigned long flags, const char *call)
 {
 	unsigned long cur_flags;
+	bool mismatch;
 
 	local_save_flags(cur_flags);
-	if (!WARN_ON_ONCE(cur_flags != flags))
+
+	mismatch = (cur_flags ^ flags) & ARCH_EFI_IRQ_FLAGS_MASK;
+	if (!WARN_ON_ONCE(mismatch))
 		return;
 
 	add_taint(TAINT_FIRMWARE_WORKAROUND, LOCKDEP_NOW_UNRELIABLE);