From: Dave Hansen <dave.han...@linux.intel.com> There are times where the kernel is entered but there is not a safe stack, like at SYSCALL entry. To obtain a safe stack, the per-CPU variables 'rsp_scratch' and 'cpu_current_top_of_stack' are used to save the old %rsp value and to find where the kernel stack should start.
You can not directly manipulate the CR3 register. You can only 'MOV' to it from another register, which means a register must be clobbered in order to do any CR3 manipulation. User-mapping these variables allows us to obtain a safe stack and use it for temporary storage *before* CR3 is switched. Signed-off-by: Dave Hansen <dave.han...@linux.intel.com> Signed-off-by: Thomas Gleixner <t...@linutronix.de> Cc: Andy Lutomirski <l...@kernel.org> Cc: Borislav Petkov <b...@alien8.de> Cc: Brian Gerst <brge...@gmail.com> Cc: Denys Vlasenko <dvlas...@redhat.com> Cc: H. Peter Anvin <h...@zytor.com> Cc: Josh Poimboeuf <jpoim...@redhat.com> Cc: Linus Torvalds <torva...@linux-foundation.org> Cc: Peter Zijlstra <pet...@infradead.org> Cc: Rik van Riel <r...@redhat.com> Cc: daniel.gr...@iaik.tugraz.at Cc: hu...@google.com Cc: keesc...@google.com Cc: linux...@kvack.org Cc: michael.schw...@iaik.tugraz.at Cc: moritz.l...@iaik.tugraz.at Cc: richard.fell...@student.tugraz.at Link: https://lkml.kernel.org/r/20171123003459.c0ff1...@viggo.jf.intel.com Signed-off-by: Ingo Molnar <mi...@kernel.org> --- arch/x86/kernel/cpu/common.c | 2 +- arch/x86/kernel/process_64.c | 2 +- 2 files changed, 2 insertions(+), 2 deletions(-) diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c index 7b348cc33e2d..f4f4ab8525bd 100644 --- a/arch/x86/kernel/cpu/common.c +++ b/arch/x86/kernel/cpu/common.c @@ -1515,7 +1515,7 @@ EXPORT_PER_CPU_SYMBOL(__preempt_count); * the top of the kernel stack. Use an extra percpu variable to track the * top of the kernel stack directly. */ -DEFINE_PER_CPU(unsigned long, cpu_current_top_of_stack) = +DEFINE_PER_CPU_USER_MAPPED(unsigned long, cpu_current_top_of_stack) = (unsigned long)&init_thread_union + THREAD_SIZE; EXPORT_PER_CPU_SYMBOL(cpu_current_top_of_stack); diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c index 157f81816915..631e229ab428 100644 --- a/arch/x86/kernel/process_64.c +++ b/arch/x86/kernel/process_64.c @@ -59,7 +59,7 @@ #include <asm/unistd_32_ia32.h> #endif -__visible DEFINE_PER_CPU(unsigned long, rsp_scratch); +__visible DEFINE_PER_CPU_USER_MAPPED(unsigned long, rsp_scratch); /* Prints also some state that isn't saved in the pt_regs */ void __show_regs(struct pt_regs *regs, int all) -- 2.14.1
