linux-kernel - [RFC PATCH 11/21] x86/xen: Add xen_cpuid() and xen_setup

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Message-Id: <c93e79a511c19969f006463c121a30d498a6ca73.1437150175.git.jpoimboe@redhat.com>
Date:	Fri, 17 Jul 2015 11:47:27 -0500
From:	Josh Poimboeuf <jpoimboe@...hat.com>
To:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>
Cc:	Michal Marek <mmarek@...e.cz>,
	Peter Zijlstra <peterz@...radead.org>,
	Andy Lutomirski <luto@...nel.org>,
	Borislav Petkov <bp@...en8.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andi Kleen <andi@...stfloor.org>,
	Pedro Alves <palves@...hat.com>, x86@...nel.org,
	live-patching@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [RFC PATCH 11/21] x86/xen: Add xen_cpuid() and xen_setup_gdt() to stackvalidate whitelists

stackvalidate reports the following false positive warnings:

  stackvalidate: arch/x86/xen/enlighten.o: xen_cpuid()+0x41: can't find jump dest instruction at .text+0x108
  stackvalidate: arch/x86/xen/enlighten.o: xen_setup_gdt.constprop.23()+0x2e: kernel entry/exit from callable instruction

The first warning is due to xen_cpuid()'s use of XEN_EMULATE_PREFIX to
insert some fake instructions which stackvalidate doesn't know how to
decode.

The second warning is due to xen_setup_gdt()'s use of an lret
instruction, which stackvalidate normally doesn't allow in callable
functions.  But this seems to be a valid use of the instruction.

Add both functions to the stackvalidate whitelist.  This results in no
actual changes to the generated code.

Signed-off-by: Josh Poimboeuf <jpoimboe@...hat.com>
---
 arch/x86/xen/enlighten.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index 32136bf..8091836 100644
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -32,6 +32,7 @@
 #include <linux/gfp.h>
 #include <linux/memblock.h>
 #include <linux/edd.h>
+#include <linux/stackvalidate.h>
 
 #include <xen/xen.h>
 #include <xen/events.h>
@@ -345,8 +346,8 @@ static void xen_cpuid(unsigned int *ax, unsigned int *bx,
 	*cx &= maskecx;
 	*cx |= setecx;
 	*dx &= maskedx;
-
 }
+STACKVALIDATE_IGNORE_FUNC(xen_cpuid);
 
 static bool __init xen_check_mwait(void)
 {
@@ -1403,6 +1404,7 @@ static void __ref xen_setup_gdt(int cpu)
 	pv_cpu_ops.write_gdt_entry = xen_write_gdt_entry;
 	pv_cpu_ops.load_gdt = xen_load_gdt;
 }
+STACKVALIDATE_IGNORE_FUNC(xen_setup_gdt);
 
 #ifdef CONFIG_XEN_PVH
 /*
-- 
2.1.0

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