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 | 9 +++++++-- arch/x86/kernel/process_32.c | 2 ++ 2 files changed, 9 insertions(+), 2 deletions(-) diff --git a/arch/x86/kernel/asm-offsets_32.c b/arch/x86/kernel/asm-offsets_32.c index 15b3f45..82826f2 100644 --- a/arch/x86/kernel/asm-offsets_32.c +++ b/arch/x86/kernel/asm-offsets_32.c @@ -46,9 +46,14 @@ void foo(void) OFFSET(saved_context_gdt_desc, saved_context, gdt_desc); BLANK(); - /* Offset from the entry stack to task stack stored in TSS */ + /* + * Offset from the entry stack to task stack stored in TSS. Kernel entry + * happens on the per-cpu entry-stack, and the asm code switches to the + * task-stack pointer stored in x86_tss.sp1, which is a copy of + * task->thread.sp0 where entry code can find it. + */ DEFINE(TSS_entry2task_stack, - offsetof(struct cpu_entry_area, tss.x86_tss.sp0) - + offsetof(struct cpu_entry_area, tss.x86_tss.sp1) - offsetofend(struct cpu_entry_area, entry_stack_page.stack)); #ifdef CONFIG_STACKPROTECTOR diff --git a/arch/x86/kernel/process_32.c b/arch/x86/kernel/process_32.c index 0ae659d..ec62cc7 100644 --- a/arch/x86/kernel/process_32.c +++ b/arch/x86/kernel/process_32.c @@ -290,6 +290,8 @@ __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
