linux-kernel - Re: [PATCH 2/4] efi: Capsule update support

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Message-ID: <20160329122658.GC3625@codeblueprint.co.uk>
Date:	Tue, 29 Mar 2016 13:26:58 +0100
From:	Matt Fleming <matt@...eblueprint.co.uk>
To:	Ard Biesheuvel <ard.biesheuvel@...aro.org>
Cc:	"linux-efi@...r.kernel.org" <linux-efi@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	joeyli <jlee@...e.com>,
	Kweh Hock Leong <hock.leong.kweh@...el.com>,
	Borislav Petkov <bp@...en8.de>,
	Mark Salter <msalter@...hat.com>,
	Peter Jones <pjones@...hat.com>,
	Bryan O'Donoghue <pure.logic@...us-software.ie>
Subject: Re: [PATCH 2/4] efi: Capsule update support

On Mon, 21 Mar, at 08:31:59PM, Matt Fleming wrote:
> 
> Good question. They're not handled in any special way with this patch
> series, so the firmware will just initiate its own reset inside of
> UpdateCapsule().
> 
> That's probably not what we want, because things like on-disk
> consistency are not guaranteed if the machine spontaneously reboots
> without assistance from the kernel.
> 
> The simplest thing to do is to refuse to pass such capsules to the
> firmware, since it's likely not going to be a common use case. But
> maybe that's overly restrictive.
> 
> Let me have a think about that one.

OK, I did think about this, and until someone actually requests the
ability to handle CAPSULE_FLAGS_INITIATE_RESET, I'm happy to just punt
on the problem. Anyone got any objections?

---

diff --git a/drivers/firmware/efi/capsule.c b/drivers/firmware/efi/capsule.c
index dac25208ad5e..84450e9cdf41 100644
--- a/drivers/firmware/efi/capsule.c
+++ b/drivers/firmware/efi/capsule.c
@@ -84,6 +84,14 @@ int efi_capsule_supported(efi_guid_t guid, u32 flags, size_t size, int *reset)
 	u64 max_size;
 	int rv = 0;
 
+	/*
+	 * We do not handle firmware-initiated reset because that
+	 * would require us to prepare the kernel for reboot. Refuse
+	 * to load any capsules with that flag.
+	 */
+	if (flags & EFI_CAPSULE_INITIATE_RESET)
+		return -EINVAL;
+
 	capsule = kmalloc(sizeof(*capsule), GFP_KERNEL);
 	if (!capsule)
 		return -ENOMEM;