linux-kernel - [PATCH 21/28] efi/x86: preserve %ebx correctly in efi_set_virtual_address

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Message-Id: <20200308080859.21568-22-ardb@kernel.org>
Date:   Sun,  8 Mar 2020 09:08:52 +0100
From:   Ard Biesheuvel <ardb@...nel.org>
To:     linux-efi@...r.kernel.org, Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>
Cc:     Ard Biesheuvel <ardb@...nel.org>, linux-kernel@...r.kernel.org,
        Arvind Sankar <nivedita@...m.mit.edu>,
        Christoph Hellwig <hch@....de>,
        David Hildenbrand <david@...hat.com>,
        Davidlohr Bueso <dave@...olabs.net>,
        Guenter Roeck <linux@...ck-us.net>,
        Heinrich Schuchardt <xypron.glpk@....de>,
        Jonathan Corbet <corbet@....net>,
        Lukas Bulwahn <lukas.bulwahn@...il.com>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Nikolai Merinov <n.merinov@...ngo-systems.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        Vladis Dronov <vdronov@...hat.com>
Subject: [PATCH 21/28] efi/x86: preserve %ebx correctly in efi_set_virtual_address_map()

Commit 59f2a619a2db8611 ("efi: Add 'runtime' pointer to struct efi")
modified the assembler routine called by efi_set_virtual_address_map(),
to grab the 'runtime' EFI service pointer while running with paging
disabled (which is tricky to do in C code)

After the change, register %ebx is not restored correctly, resulting
in all kinds of weird behavior, so fix that.

Reported-by: Guenter Roeck <linux@...ck-us.net>
Tested-by: Guenter Roeck <linux@...ck-us.net>
Link: https://lore.kernel.org/r/20200304133515.15035-1-ardb@kernel.org
Signed-off-by: Ard Biesheuvel <ardb@...nel.org>
---
 arch/x86/platform/efi/efi_stub_32.S | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/platform/efi/efi_stub_32.S b/arch/x86/platform/efi/efi_stub_32.S
index 09237236fb25..09ec84f6ef51 100644
--- a/arch/x86/platform/efi/efi_stub_32.S
+++ b/arch/x86/platform/efi/efi_stub_32.S
@@ -54,7 +54,7 @@ SYM_FUNC_START(efi_call_svam)
 	orl	$0x80000000, %edx
 	movl	%edx, %cr0
 
-	pop	%ebx
+	movl	16(%esp), %ebx
 	leave
 	ret
 SYM_FUNC_END(efi_call_svam)
-- 
2.17.1