[PATCH 03/31] x86/entry/32: Load task stack from x86_tss.sp1 in SYSENTER handler

[Joerg Roedel]

From: Joerg Roedel <jroedel@xxxxxxx>

We want x86_tss.sp0 point to the entry stack later to use
it as a trampoline stack for other kernel entry points
besides SYSENTER.

So store the task stack pointer in x86_tss.sp1, which is
otherwise unused by the hardware, as Linux doesn't make use
of Ring 1.

Signed-off-by: Joerg Roedel <jroedel@xxxxxxx>
---
 arch/x86/kernel/asm-offsets_32.c | 2 +-
 arch/x86/kernel/process_32.c     | 2 ++
 2 files changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/asm-offsets_32.c b/arch/x86/kernel/asm-offsets_32.c
index f452bfd..b97e48c 100644
--- a/arch/x86/kernel/asm-offsets_32.c
+++ b/arch/x86/kernel/asm-offsets_32.c
@@ -47,7 +47,7 @@ void foo(void)
 	BLANK();
 
 	/* Offset from the sysenter stack to tss.sp0 */
-	DEFINE(TSS_entry_stack, offsetof(struct cpu_entry_area, tss.x86_tss.sp0) -
+	DEFINE(TSS_entry_stack, offsetof(struct cpu_entry_area, tss.x86_tss.sp1) -
 	       offsetofend(struct cpu_entry_area, entry_stack_page.stack));
 
 #ifdef CONFIG_CC_STACKPROTECTOR
diff --git a/arch/x86/kernel/process_32.c b/arch/x86/kernel/process_32.c
index 5224c60..097d36a 100644
--- a/arch/x86/kernel/process_32.c
+++ b/arch/x86/kernel/process_32.c
@@ -292,6 +292,8 @@ __switch_to(struct task_struct *prev_p, struct task_struct *next_p)
 	this_cpu_write(cpu_current_top_of_stack,
 		       (unsigned long)task_stack_page(next_p) +
 		       THREAD_SIZE);
+	/* SYSENTER reads the task-stack from tss.sp1 */
+	this_cpu_write(cpu_tss_rw.x86_tss.sp1, next_p->thread.sp0);
 
 	/*
 	 * Restore %gs if needed (which is common)
-- 
2.7.4