[PATCH 04/23] x86, kaiser: mark per-cpu data structures required for entry/exit

Dave Hansen
2017-11-23T00:45:46Z

From: Dave Hansen <dave.hansen@linux.intel.com>

These patches are based on work from a team at Graz University of
Technology posted here: https://github.com/IAIK/KAISER

The KAISER approach keeps two copies of the page tables: one for running
in the kernel and one for running userspace. But, there are a few
structures that are needed for switching in and out of the kernel and
a good subset of *those* are per-cpu data.

Here's a short summary of the things mapped to userspace:
* The gdt_page's virtual address is pointed to by the LGDT instruction.
It is needed to define the segments. Deeply required by CPU to run.
* cpu_tss tells the CPU, among other things, where the new stacks are
after user<->kernel transitions. Needed by the CPU to make ring
transitions.
* exception_stacks are needed at interrupt and exception entry
so that there is storage for, among other things, some temporary
space to permit clobbering a register to load the kernel CR3.

Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Moritz Lipp <moritz.lipp@iaik.tugraz.at>
Cc: Daniel Gruss <daniel.gruss@iaik.tugraz.at>
Cc: Michael Schwarz <michael.schwarz@iaik.tugraz.at>
Cc: Richard Fellner <richard.fellner@student.tugraz.at>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Kees Cook <keescook@google.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: x86@kernel.org
---

b/arch/x86/include/asm/desc.h | 2 +-
b/arch/x86/include/asm/processor.h | 2 +-
b/arch/x86/kernel/cpu/common.c | 4 ++--
b/arch/x86/kernel/process.c | 2 +-
4 files changed, 5 insertions(+), 5 deletions(-)

diff -puN arch/x86/include/asm/desc.h~kaiser-prep-x86-percpu-user-mapped arch/x86/include/asm/desc.h
--- a/arch/x86/include/asm/desc.h~kaiser-prep-x86-percpu-user-mapped 2017-11-22 15:45:45.913619747 -0800
+++ b/arch/x86/include/asm/desc.h 2017-11-22 15:45:45.923619747 -0800
@@ -46,7 +46,7 @@ struct gdt_page {
struct desc_struct gdt[GDT_ENTRIES];
} __attribute__((aligned(PAGE_SIZE)));

-DECLARE_PER_CPU_PAGE_ALIGNED(struct gdt_page, gdt_page);
+DECLARE_PER_CPU_PAGE_ALIGNED_USER_MAPPED(struct gdt_page, gdt_page);

/* Provide the original GDT */
static inline struct desc_struct *get_cpu_gdt_rw(unsigned int cpu)
diff -puN arch/x86/include/asm/processor.h~kaiser-prep-x86-percpu-user-mapped arch/x86/include/asm/processor.h
--- a/arch/x86/include/asm/processor.h~kaiser-prep-x86-percpu-user-mapped 2017-11-22 15:45:45.915619747 -0800
+++ b/arch/x86/include/asm/processor.h 2017-11-22 15:45:45.923619747 -0800
@@ -356,7 +356,7 @@ struct tss_struct {
unsigned long io_bitmap[IO_BITMAP_LONGS + 1];
} __attribute__((__aligned__(PAGE_SIZE)));

-DECLARE_PER_CPU_PAGE_ALIGNED(struct tss_struct, cpu_tss);
+DECLARE_PER_CPU_PAGE_ALIGNED_USER_MAPPED(struct tss_struct, cpu_tss);

/*
* sizeof(unsigned long) coming from an extra "long" at the end
diff -puN arch/x86/kernel/cpu/common.c~kaiser-prep-x86-percpu-user-mapped arch/x86/kernel/cpu/common.c
--- a/arch/x86/kernel/cpu/common.c~kaiser-prep-x86-percpu-user-mapped 2017-11-22 15:45:45.917619747 -0800
+++ b/arch/x86/kernel/cpu/common.c 2017-11-22 15:45:45.924619747 -0800
@@ -98,7 +98,7 @@ static const struct cpu_dev default_cpu

static const struct cpu_dev *this_cpu = &default_cpu;

-DEFINE_PER_CPU_PAGE_ALIGNED(struct gdt_page, gdt_page) = { .gdt = {
+DEFINE_PER_CPU_PAGE_ALIGNED_USER_MAPPED(struct gdt_page, gdt_page) = { .gdt = {
#ifdef CONFIG_X86_64
/*
* We need valid kernel segments for data and code in long mode too
@@ -517,7 +517,7 @@ static const unsigned int exception_stac
[DEBUG_STACK - 1] = DEBUG_STKSZ
};

-static DEFINE_PER_CPU_PAGE_ALIGNED(char, exception_stacks
+DEFINE_PER_CPU_PAGE_ALIGNED_USER_MAPPED(char, exception_stacks
[(N_EXCEPTION_STACKS - 1) * EXCEPTION_STKSZ + DEBUG_STKSZ]);
#endif

diff -puN arch/x86/kernel/process.c~kaiser-prep-x86-percpu-user-mapped arch/x86/kernel/process.c
--- a/arch/x86/kernel/process.c~kaiser-prep-x86-percpu-user-mapped 2017-11-22 15:45:45.919619747 -0800
+++ b/arch/x86/kernel/process.c 2017-11-22 15:45:45.924619747 -0800
@@ -47,7 +47,7 @@
* section. Since TSS's are completely CPU-local, we want them
* on exact cacheline boundaries, to eliminate cacheline ping-pong.
*/
-__visible DEFINE_PER_CPU_SHARED_ALIGNED(struct tss_struct, cpu_tss) = {
+__visible DEFINE_PER_CPU_SHARED_ALIGNED_USER_MAPPED(struct tss_struct, cpu_tss) = {
.x86_tss = {
/*
* .sp0 is only used when entering ring 0 from a lower
_