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x86/asm/entry/64: Save user RSP in pt_regs->sp on SYSCALL64 fastpath

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Prepare for the removal of 'usersp', by simplifying PER_CPU(old_rsp) usage:

  - use it only as temp storage

  - store the userspace stack pointer immediately in pt_regs->sp
    on syscall entry, instead of using it later, on syscall exit.

  - change C code to use pt_regs->sp only, instead of PER_CPU(old_rsp)
    and task->thread.usersp.

FIXUP/RESTORE_TOP_OF_STACK are simplified as well.

Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Alexei Starovoitov <ast@plumgrid.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Will Drewry <wad@chromium.org>
Link: http://lkml.kernel.org/r/1425926364-9526-4-git-send-email-dvlasenk@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Denys Vlasenko 2015-03-09 19:39:23 +01:00 committed by Ingo Molnar
parent 616ab249f1
commit 263042e463
5 changed files with 12 additions and 21 deletions
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2
arch/x86/include/asm/compat.h
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@ -301,7 +301,7 @@ static inline void __user *arch_compat_alloc_user_space(long len)
sp = task_pt_regs(current)->sp;
} else {
/* -128 for the x32 ABI redzone */
sp = this_cpu_read(old_rsp) - 128;
sp = task_pt_regs(current)->sp - 128;
}
return (void __user *)round_down(sp - len, 16);

8
arch/x86/include/asm/ptrace.h
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@ -145,12 +145,8 @@ static inline bool user_64bit_mode(struct pt_regs *regs)
#endif
}
#define current_user_stack_pointer() this_cpu_read(old_rsp)
/* ia32 vs. x32 difference */
#define compat_user_stack_pointer() \
(test_thread_flag(TIF_IA32) \
? current_pt_regs()->sp \
: this_cpu_read(old_rsp))
#define current_user_stack_pointer() current_pt_regs()->sp
#define compat_user_stack_pointer() current_pt_regs()->sp
#endif
#ifdef CONFIG_X86_32

18
arch/x86/kernel/entry_64.S
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@ -128,8 +128,6 @@ ENDPROC(native_usergs_sysret64)
* manipulation.
*/
.macro FIXUP_TOP_OF_STACK tmp offset=0
movq PER_CPU_VAR(old_rsp),\tmp
movq \tmp,RSP+\offset(%rsp)
movq $__USER_DS,SS+\offset(%rsp)
movq $__USER_CS,CS+\offset(%rsp)
movq RIP+\offset(%rsp),\tmp /* get rip */
@ -139,8 +137,7 @@ ENDPROC(native_usergs_sysret64)
.endm
.macro RESTORE_TOP_OF_STACK tmp offset=0
movq RSP+\offset(%rsp),\tmp
movq \tmp,PER_CPU_VAR(old_rsp)
/* nothing to do */
.endm
/*
@ -222,9 +219,6 @@ ENDPROC(native_usergs_sysret64)
* Interrupts are off on entry.
* Only called from user space.
*
* XXX if we had a free scratch register we could save the RSP into the stack frame
* and report it properly in ps. Unfortunately we haven't.
*
* When user can change the frames always force IRET. That is because
* it deals with uncanonical addresses better. SYSRET has trouble
* with them due to bugs in both AMD and Intel CPUs.
@ -253,11 +247,13 @@ GLOBAL(system_call_after_swapgs)
*/
ENABLE_INTERRUPTS(CLBR_NONE)
ALLOC_PT_GPREGS_ON_STACK 8 /* +8: space for orig_ax */
movq %rcx,RIP(%rsp)
movq PER_CPU_VAR(old_rsp),%rcx
movq %r11,EFLAGS(%rsp)
movq %rcx,RSP(%rsp)
movq_cfi rax,ORIG_RAX
SAVE_C_REGS_EXCEPT_RAX_RCX_R11
movq $-ENOSYS,RAX(%rsp)
movq_cfi rax,ORIG_RAX
movq %r11,EFLAGS(%rsp)
movq %rcx,RIP(%rsp)
CFI_REL_OFFSET rip,RIP
testl $_TIF_WORK_SYSCALL_ENTRY,TI_flags+THREAD_INFO(%rsp,RIP)
jnz tracesys
@ -293,7 +289,7 @@ ret_from_sys_call:
CFI_REGISTER rip,rcx
movq EFLAGS(%rsp),%r11
/*CFI_REGISTER rflags,r11*/
movq PER_CPU_VAR(old_rsp), %rsp
movq RSP(%rsp),%rsp
/*
* 64bit SYSRET restores rip from rcx,
* rflags from r11 (but RF and VM bits are forced to 0),

2
arch/x86/kernel/perf_regs.c
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@ -177,7 +177,7 @@ void perf_get_regs_user(struct perf_regs *regs_user,
* than just blindly copying user_regs.
*/
regs_user->abi = PERF_SAMPLE_REGS_ABI_64;
regs_user_copy->sp = this_cpu_read(old_rsp);
regs_user_copy->sp = user_regs->sp;
regs_user_copy->cs = __USER_CS;
regs_user_copy->ss = __USER_DS;
regs_user_copy->cx = -1; /* usually contains garbage */

3
arch/x86/kernel/process_64.c
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@ -602,6 +602,5 @@ long sys_arch_prctl(int code, unsigned long addr)
unsigned long KSTK_ESP(struct task_struct *task)
{
return (test_tsk_thread_flag(task, TIF_IA32)) ?
(task_pt_regs(task)->sp) : ((task)->thread.usersp);
return task_pt_regs(task)->sp;
}