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x86/entry/64: Use the TSS sp2 slot for SYSCALL/SYSRET scratch space

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In the non-trampoline SYSCALL64 path, a percpu variable is used to
temporarily store the user RSP value.

Instead of a separate variable, use the otherwise unused sp2 slot in the
TSS.  This will improve cache locality, as the sp1 slot is already used in
the same code to find the kernel stack.  It will also simplify a future
change to make the non-trampoline path work in PTI mode.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Borislav Petkov <bp@suse.de>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Joerg Roedel <joro@8bytes.org>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lkml.kernel.org/r/08e769a0023dbad4bac6f34f3631dbaf8ad59f4f.1536015544.git.luto@kernel.org
This commit is contained in:
Andy Lutomirski 2018-09-03 15:59:43 -07:00 committed by Thomas Gleixner
parent bd7b1f7cbf
commit 98f05b5138
5 changed files with 22 additions and 13 deletions
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16
arch/x86/entry/entry_64.S
View File

@ -215,18 +215,20 @@ ENTRY(entry_SYSCALL_64)
/*
* This path is only taken when PAGE_TABLE_ISOLATION is disabled so it
* is not required to switch CR3.
*
* tss.sp2 is scratch space.
*/
movq %rsp, PER_CPU_VAR(rsp_scratch)
movq %rsp, PER_CPU_VAR(cpu_tss_rw + TSS_sp2)
movq PER_CPU_VAR(cpu_current_top_of_stack), %rsp
/* Construct struct pt_regs on stack */
pushq $__USER_DS /* pt_regs->ss */
pushq PER_CPU_VAR(rsp_scratch) /* pt_regs->sp */
pushq %r11 /* pt_regs->flags */
pushq $__USER_CS /* pt_regs->cs */
pushq %rcx /* pt_regs->ip */
pushq $__USER_DS /* pt_regs->ss */
pushq PER_CPU_VAR(cpu_tss_rw + TSS_sp2) /* pt_regs->sp */
pushq %r11 /* pt_regs->flags */
pushq $__USER_CS /* pt_regs->cs */
pushq %rcx /* pt_regs->ip */
GLOBAL(entry_SYSCALL_64_after_hwframe)
pushq %rax /* pt_regs->orig_ax */
pushq %rax /* pt_regs->orig_ax */
PUSH_AND_CLEAR_REGS rax=$-ENOSYS

6
arch/x86/include/asm/processor.h
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@ -315,7 +315,13 @@ struct x86_hw_tss {
*/
u64 sp1;
/*
* Since Linux does not use ring 2, the 'sp2' slot is unused by
* hardware. entry_SYSCALL_64 uses it as scratch space to stash
* the user RSP value.
*/
u64 sp2;
u64 reserved2;
u64 ist[7];
u32 reserved3;

3
arch/x86/kernel/asm-offsets.c
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@ -105,7 +105,8 @@ void common(void) {
DEFINE(SIZEOF_entry_stack, sizeof(struct entry_stack));
DEFINE(MASK_entry_stack, (~(sizeof(struct entry_stack) - 1)));
/* Offset for sp0 and sp1 into the tss_struct */
/* Offset for fields in tss_struct */
OFFSET(TSS_sp0, tss_struct, x86_tss.sp0);
OFFSET(TSS_sp1, tss_struct, x86_tss.sp1);
OFFSET(TSS_sp2, tss_struct, x86_tss.sp2);
}

2
arch/x86/kernel/process_64.c
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@ -59,8 +59,6 @@
#include <asm/unistd_32_ia32.h>
#endif
__visible DEFINE_PER_CPU(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)
{

8
arch/x86/xen/xen-asm_64.S
View File

@ -91,13 +91,15 @@ ENTRY(xen_iret)
ENTRY(xen_sysret64)
/*
* We're already on the usermode stack at this point, but
* still with the kernel gs, so we can easily switch back
* still with the kernel gs, so we can easily switch back.
*
* tss.sp2 is scratch space.
*/
movq %rsp, PER_CPU_VAR(rsp_scratch)
movq %rsp, PER_CPU_VAR(cpu_tss_rw + TSS_sp2)
movq PER_CPU_VAR(cpu_current_top_of_stack), %rsp
pushq $__USER_DS
pushq PER_CPU_VAR(rsp_scratch)
pushq PER_CPU_VAR(cpu_tss_rw + TSS_sp2)
pushq %r11
pushq $__USER_CS
pushq %rcx