x86/fsgsbase/64: Introduce FS/GS base helper functions
Introduce FS/GS base access functionality via <asm/fsgsbase.h>, not yet used by anything directly. Factor out task_seg_base() from x86/ptrace.c and rename it to x86_fsgsbase_read_task() to make it part of the new helpers. This will allow us to enhance FSGSBASE support and eventually enable the FSBASE/GSBASE instructions. An "inactive" GS base refers to a base saved at kernel entry and being part of an inactive, non-running/stopped user-task. (The typical ptrace model.) Here are the new functions: x86_fsbase_read_task() x86_gsbase_read_task() x86_fsbase_write_task() x86_gsbase_write_task() x86_fsbase_read_cpu() x86_fsbase_write_cpu() x86_gsbase_read_cpu_inactive() x86_gsbase_write_cpu_inactive() As an advantage of the unified namespace we can now see all FS/GSBASE API use in the kernel via the following 'git grep' pattern: $ git grep x86_.*sbase [ mingo: Wrote new changelog. ] Based-on-code-from: Andy Lutomirski <luto@kernel.org> Suggested-by: Ingo Molnar <mingo@kernel.org> Signed-off-by: Chang S. Bae <chang.seok.bae@intel.com> Cc: Andy Lutomirski <luto@amacapital.net> Cc: Andy Lutomirski <luto@kernel.org> Cc: Borislav Petkov <bp@alien8.de> Cc: Brian Gerst <brgerst@gmail.com> Cc: Dave Hansen <dave.hansen@linux.intel.com> Cc: Denys Vlasenko <dvlasenk@redhat.com> Cc: H. Peter Anvin <hpa@zytor.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Markus T Metzger <markus.t.metzger@intel.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Ravi Shankar <ravi.v.shankar@intel.com> Cc: Rik van Riel <riel@surriel.com> Cc: Thomas Gleixner <tglx@linutronix.de> Link: http://lkml.kernel.org/r/1537312139-5580-3-git-send-email-chang.seok.bae@intel.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Chang S. Bae
Ingo Molnar
Родитель
07e1d88ada
Коммит
b1378a561f
|
|
@ -0,0 +1,50 @@
|
|||
/* SPDX-License-Identifier: GPL-2.0 */
|
||||
#ifndef _ASM_FSGSBASE_H
|
||||
#define _ASM_FSGSBASE_H 1
|
||||
|
||||
#ifndef __ASSEMBLY__
|
||||
|
||||
#ifdef CONFIG_X86_64
|
||||
|
||||
#include <asm/msr-index.h>
|
||||
|
||||
unsigned long x86_fsgsbase_read_task(struct task_struct *task,
|
||||
unsigned short selector);
|
||||
|
||||
/*
|
||||
* Read/write a task's fsbase or gsbase. This returns the value that
|
||||
* the FS/GS base would have (if the task were to be resumed). These
|
||||
* work on current or on a different non-running task.
|
||||
*/
|
||||
unsigned long x86_fsbase_read_task(struct task_struct *task);
|
||||
unsigned long x86_gsbase_read_task(struct task_struct *task);
|
||||
int x86_fsbase_write_task(struct task_struct *task, unsigned long fsbase);
|
||||
int x86_gsbase_write_task(struct task_struct *task, unsigned long gsbase);
|
||||
|
||||
/* Helper functions for reading/writing FS/GS base */
|
||||
|
||||
static inline unsigned long x86_fsbase_read_cpu(void)
|
||||
{
|
||||
unsigned long fsbase;
|
||||
|
||||
rdmsrl(MSR_FS_BASE, fsbase);
|
||||
return fsbase;
|
||||
}
|
||||
|
||||
void x86_fsbase_write_cpu(unsigned long fsbase);
|
||||
|
||||
static inline unsigned long x86_gsbase_read_cpu_inactive(void)
|
||||
{
|
||||
unsigned long gsbase;
|
||||
|
||||
rdmsrl(MSR_KERNEL_GS_BASE, gsbase);
|
||||
return gsbase;
|
||||
}
|
||||
|
||||
void x86_gsbase_write_cpu_inactive(unsigned long gsbase);
|
||||
|
||||
#endif /* CONFIG_X86_64 */
|
||||
|
||||
#endif /* __ASSEMBLY__ */
|
||||
|
||||
#endif /* _ASM_FSGSBASE_H */
|
||||
|
|
@ -54,6 +54,7 @@
|
|||
#include <asm/vdso.h>
|
||||
#include <asm/intel_rdt_sched.h>
|
||||
#include <asm/unistd.h>
|
||||
#include <asm/fsgsbase.h>
|
||||
#ifdef CONFIG_IA32_EMULATION
|
||||
/* Not included via unistd.h */
|
||||
#include <asm/unistd_32_ia32.h>
|
||||
|
|
@ -286,6 +287,129 @@ static __always_inline void load_seg_legacy(unsigned short prev_index,
|
|||
}
|
||||
}
|
||||
|
||||
unsigned long x86_fsgsbase_read_task(struct task_struct *task,
|
||||
unsigned short selector)
|
||||
{
|
||||
unsigned short idx = selector >> 3;
|
||||
unsigned long base;
|
||||
|
||||
if (likely((selector & SEGMENT_TI_MASK) == 0)) {
|
||||
if (unlikely(idx >= GDT_ENTRIES))
|
||||
return 0;
|
||||
|
||||
/*
|
||||
* There are no user segments in the GDT with nonzero bases
|
||||
* other than the TLS segments.
|
||||
*/
|
||||
if (idx < GDT_ENTRY_TLS_MIN || idx > GDT_ENTRY_TLS_MAX)
|
||||
return 0;
|
||||
|
||||
idx -= GDT_ENTRY_TLS_MIN;
|
||||
base = get_desc_base(&task->thread.tls_array[idx]);
|
||||
} else {
|
||||
#ifdef CONFIG_MODIFY_LDT_SYSCALL
|
||||
struct ldt_struct *ldt;
|
||||
|
||||
/*
|
||||
* If performance here mattered, we could protect the LDT
|
||||
* with RCU. This is a slow path, though, so we can just
|
||||
* take the mutex.
|
||||
*/
|
||||
mutex_lock(&task->mm->context.lock);
|
||||
ldt = task->mm->context.ldt;
|
||||
if (unlikely(idx >= ldt->nr_entries))
|
||||
base = 0;
|
||||
else
|
||||
base = get_desc_base(ldt->entries + idx);
|
||||
mutex_unlock(&task->mm->context.lock);
|
||||
#else
|
||||
base = 0;
|
||||
#endif
|
||||
}
|
||||
|
||||
return base;
|
||||
}
|
||||
|
||||
void x86_fsbase_write_cpu(unsigned long fsbase)
|
||||
{
|
||||
/*
|
||||
* Set the selector to 0 as a notion, that the segment base is
|
||||
* overwritten, which will be checked for skipping the segment load
|
||||
* during context switch.
|
||||
*/
|
||||
loadseg(FS, 0);
|
||||
wrmsrl(MSR_FS_BASE, fsbase);
|
||||
}
|
||||
|
||||
void x86_gsbase_write_cpu_inactive(unsigned long gsbase)
|
||||
{
|
||||
/* Set the selector to 0 for the same reason as %fs above. */
|
||||
loadseg(GS, 0);
|
||||
wrmsrl(MSR_KERNEL_GS_BASE, gsbase);
|
||||
}
|
||||
|
||||
unsigned long x86_fsbase_read_task(struct task_struct *task)
|
||||
{
|
||||
unsigned long fsbase;
|
||||
|
||||
if (task == current)
|
||||
fsbase = x86_fsbase_read_cpu();
|
||||
else if (task->thread.fsindex == 0)
|
||||
fsbase = task->thread.fsbase;
|
||||
else
|
||||
fsbase = x86_fsgsbase_read_task(task, task->thread.fsindex);
|
||||
|
||||
return fsbase;
|
||||
}
|
||||
|
||||
unsigned long x86_gsbase_read_task(struct task_struct *task)
|
||||
{
|
||||
unsigned long gsbase;
|
||||
|
||||
if (task == current)
|
||||
gsbase = x86_gsbase_read_cpu_inactive();
|
||||
else if (task->thread.gsindex == 0)
|
||||
gsbase = task->thread.gsbase;
|
||||
else
|
||||
gsbase = x86_fsgsbase_read_task(task, task->thread.gsindex);
|
||||
|
||||
return gsbase;
|
||||
}
|
||||
|
||||
int x86_fsbase_write_task(struct task_struct *task, unsigned long fsbase)
|
||||
{
|
||||
/*
|
||||
* Not strictly needed for %fs, but do it for symmetry
|
||||
* with %gs
|
||||
*/
|
||||
if (unlikely(fsbase >= TASK_SIZE_MAX))
|
||||
return -EPERM;
|
||||
|
||||
preempt_disable();
|
||||
task->thread.fsbase = fsbase;
|
||||
if (task == current)
|
||||
x86_fsbase_write_cpu(fsbase);
|
||||
task->thread.fsindex = 0;
|
||||
preempt_enable();
|
||||
|
||||
return 0;
|
||||
}
|
||||
|
||||
int x86_gsbase_write_task(struct task_struct *task, unsigned long gsbase)
|
||||
{
|
||||
if (unlikely(gsbase >= TASK_SIZE_MAX))
|
||||
return -EPERM;
|
||||
|
||||
preempt_disable();
|
||||
task->thread.gsbase = gsbase;
|
||||
if (task == current)
|
||||
x86_gsbase_write_cpu_inactive(gsbase);
|
||||
task->thread.gsindex = 0;
|
||||
preempt_enable();
|
||||
|
||||
return 0;
|
||||
}
|
||||
|
||||
int copy_thread_tls(unsigned long clone_flags, unsigned long sp,
|
||||
unsigned long arg, struct task_struct *p, unsigned long tls)
|
||||
{
|
||||
|
|
|
|||
|
|
@ -39,7 +39,7 @@
|
|||
#include <asm/hw_breakpoint.h>
|
||||
#include <asm/traps.h>
|
||||
#include <asm/syscall.h>
|
||||
#include <asm/mmu_context.h>
|
||||
#include <asm/fsgsbase.h>
|
||||
|
||||
#include "tls.h"
|
||||
|
||||
|
|
@ -343,49 +343,6 @@ static int set_segment_reg(struct task_struct *task,
|
|||
return 0;
|
||||
}
|
||||
|
||||
static unsigned long task_seg_base(struct task_struct *task,
|
||||
unsigned short selector)
|
||||
{
|
||||
unsigned short idx = selector >> 3;
|
||||
unsigned long base;
|
||||
|
||||
if (likely((selector & SEGMENT_TI_MASK) == 0)) {
|
||||
if (unlikely(idx >= GDT_ENTRIES))
|
||||
return 0;
|
||||
|
||||
/*
|
||||
* There are no user segments in the GDT with nonzero bases
|
||||
* other than the TLS segments.
|
||||
*/
|
||||
if (idx < GDT_ENTRY_TLS_MIN || idx > GDT_ENTRY_TLS_MAX)
|
||||
return 0;
|
||||
|
||||
idx -= GDT_ENTRY_TLS_MIN;
|
||||
base = get_desc_base(&task->thread.tls_array[idx]);
|
||||
} else {
|
||||
#ifdef CONFIG_MODIFY_LDT_SYSCALL
|
||||
struct ldt_struct *ldt;
|
||||
|
||||
/*
|
||||
* If performance here mattered, we could protect the LDT
|
||||
* with RCU. This is a slow path, though, so we can just
|
||||
* take the mutex.
|
||||
*/
|
||||
mutex_lock(&task->mm->context.lock);
|
||||
ldt = task->mm->context.ldt;
|
||||
if (unlikely(idx >= ldt->nr_entries))
|
||||
base = 0;
|
||||
else
|
||||
base = get_desc_base(ldt->entries + idx);
|
||||
mutex_unlock(&task->mm->context.lock);
|
||||
#else
|
||||
base = 0;
|
||||
#endif
|
||||
}
|
||||
|
||||
return base;
|
||||
}
|
||||
|
||||
#endif /* CONFIG_X86_32 */
|
||||
|
||||
static unsigned long get_flags(struct task_struct *task)
|
||||
|
|
@ -482,13 +439,15 @@ static unsigned long getreg(struct task_struct *task, unsigned long offset)
|
|||
if (task->thread.fsindex == 0)
|
||||
return task->thread.fsbase;
|
||||
else
|
||||
return task_seg_base(task, task->thread.fsindex);
|
||||
return x86_fsgsbase_read_task(task,
|
||||
task->thread.fsindex);
|
||||
}
|
||||
case offsetof(struct user_regs_struct, gs_base): {
|
||||
if (task->thread.gsindex == 0)
|
||||
return task->thread.gsbase;
|
||||
else
|
||||
return task_seg_base(task, task->thread.gsindex);
|
||||
return x86_fsgsbase_read_task(task,
|
||||
task->thread.gsindex);
|
||||
}
|
||||
#endif
|
||||
}
|
||||
|
|
|
|||
Загрузка…
Ссылка в новой задаче