linux-kernel - [PATCH 2/5] x86/entry/64, entry: Set up a valid sysenter stack and prepare for 32-bit merge

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Message-Id: <1287f683e32f1bbe7fc545bff675f30dcda8d5c1.1437665045.git.luto@kernel.org>
Date:	Thu, 23 Jul 2015 08:31:40 -0700
From:	Andy Lutomirski <luto@...nel.org>
To:	X86 ML <x86@...nel.org>, linux-kernel@...r.kernel.org
Cc:	Steven Rostedt <rostedt@...dmis.org>, Willy Tarreau <w@....eu>,
	Borislav Petkov <bp@...en8.de>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andy Lutomirski <luto@...nel.org>
Subject: [PATCH 2/5] x86/entry/64, entry: Set up a valid sysenter stack and prepare for 32-bit merge

Oddly, 64-bit kernels already allocate a percpu sysenter stack, but
they don't enable it.  Enable the stack and tweak the rest of the
sysenter setup code to be similar to the 32-bit version.

This eliminates the only place in the kernel in which TF could be set
without a valid stack.

Signed-off-by: Andy Lutomirski <luto@...nel.org>
---
 arch/x86/kernel/cpu/common.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 9b3a43583f81..fba86ed46aa6 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -1193,9 +1193,11 @@ void syscall_init(void)
 	 * This does not cause SYSENTER to jump to the wrong location, because
 	 * AMD doesn't allow SYSENTER in long mode (either 32- or 64-bit).
 	 */
-	wrmsrl_safe(MSR_IA32_SYSENTER_CS, (u64)__KERNEL_CS);
-	wrmsrl_safe(MSR_IA32_SYSENTER_ESP, 0ULL);
-	wrmsrl_safe(MSR_IA32_SYSENTER_EIP, (u64)entry_SYSENTER_compat);
+	wrmsrl_safe(MSR_IA32_SYSENTER_CS, __KERNEL_CS);
+	wrmsrl_safe(MSR_IA32_SYSENTER_ESP,
+		    (unsigned long)&per_cpu(cpu_tss, smp_processor_id()) +
+		    offsetofend(struct tss_struct, SYSENTER_stack));
+	wrmsrl_safe(MSR_IA32_SYSENTER_EIP, (unsigned long)entry_SYSENTER_compat);
 #else
 	wrmsrl(MSR_CSTAR, ignore_sysret);
 	wrmsrl_safe(MSR_IA32_SYSENTER_CS, (u64)GDT_ENTRY_INVALID_SEG);
-- 
2.4.3

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