[tip:x86/asm] x86/fsgsbase/64: Make ptrace use the new FS/GS base helpers

From: tip-bot for Chang S. Bae
Date: Mon Oct 08 2018 - 05:56:44 EST

Commit-ID: e696c231bebf5f17fe0c5e465c01511320668054
Gitweb: https://git.kernel.org/tip/e696c231bebf5f17fe0c5e465c01511320668054
Author: Chang S. Bae <chang.seok.bae@xxxxxxxxx>
AuthorDate: Tue, 18 Sep 2018 16:08:54 -0700
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Mon, 8 Oct 2018 10:41:08 +0200

x86/fsgsbase/64: Make ptrace use the new FS/GS base helpers

Use the new FS/GS base helper functions in <asm/fsgsbase.h> in the platform
specific ptrace implementation of the following APIs:

PTRACE_ARCH_PRCTL,
PTRACE_SETREG,
PTRACE_GETREG,
etc.

The fsgsbase code is more abstracted out this way and the FS/GS-update
mechanism will be easier to change this way.

[ mingo: Wrote new changelog. ]

Based-on-code-from: Andy Lutomirski <luto@xxxxxxxxxx>
Signed-off-by: Chang S. Bae <chang.seok.bae@xxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Brian Gerst <brgerst@xxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Cc: Denys Vlasenko <dvlasenk@xxxxxxxxxx>
Cc: H. Peter Anvin <hpa@xxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Markus T Metzger <markus.t.metzger@xxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Ravi Shankar <ravi.v.shankar@xxxxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/1537312139-5580-4-git-send-email-chang.seok.bae@xxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
arch/x86/include/asm/fsgsbase.h | 3 ---
arch/x86/kernel/process_64.c | 49 +++++++++--------------------------------
arch/x86/kernel/ptrace.c | 27 +++++++----------------
3 files changed, 18 insertions(+), 61 deletions(-)

diff --git a/arch/x86/include/asm/fsgsbase.h b/arch/x86/include/asm/fsgsbase.h
index 1ab465ee23fe..5e9cbcce318a 100644
--- a/arch/x86/include/asm/fsgsbase.h
+++ b/arch/x86/include/asm/fsgsbase.h
@@ -8,9 +8,6 @@

#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
diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
index 2a53ff8d1baf..e5fb0c3dee4d 100644
--- a/arch/x86/kernel/process_64.c
+++ b/arch/x86/kernel/process_64.c
@@ -287,8 +287,8 @@ static __always_inline void load_seg_legacy(unsigned short prev_index,
}
}

-unsigned long x86_fsgsbase_read_task(struct task_struct *task,
- unsigned short selector)
+static unsigned long x86_fsgsbase_read_task(struct task_struct *task,
+ unsigned short selector)
{
unsigned short idx = selector >> 3;
unsigned long base;
@@ -751,54 +751,25 @@ static long prctl_map_vdso(const struct vdso_image *image, unsigned long addr)
long do_arch_prctl_64(struct task_struct *task, int option, unsigned long arg2)
{
int ret = 0;
- int doit = task == current;
- int cpu;

switch (option) {
- case ARCH_SET_GS:
- if (arg2 >= TASK_SIZE_MAX)
- return -EPERM;
- cpu = get_cpu();
- task->thread.gsindex = 0;
- task->thread.gsbase = arg2;
- if (doit) {
- load_gs_index(0);
- ret = wrmsrl_safe(MSR_KERNEL_GS_BASE, arg2);
- }
- put_cpu();
+ case ARCH_SET_GS: {
+ ret = x86_gsbase_write_task(task, arg2);
break;
- case ARCH_SET_FS:
- /* Not strictly needed for fs, but do it for symmetry
- with gs */
- if (arg2 >= TASK_SIZE_MAX)
- return -EPERM;
- cpu = get_cpu();
- task->thread.fsindex = 0;
- task->thread.fsbase = arg2;
- if (doit) {
- /* set the selector to 0 to not confuse __switch_to */
- loadsegment(fs, 0);
- ret = wrmsrl_safe(MSR_FS_BASE, arg2);
- }
- put_cpu();
+ }
+ case ARCH_SET_FS: {
+ ret = x86_fsbase_write_task(task, arg2);
break;
+ }
case ARCH_GET_FS: {
- unsigned long base;
+ unsigned long base = x86_fsbase_read_task(task);

- if (doit)
- rdmsrl(MSR_FS_BASE, base);
- else
- base = task->thread.fsbase;
ret = put_user(base, (unsigned long __user *)arg2);
break;
}
case ARCH_GET_GS: {
- unsigned long base;
+ unsigned long base = x86_gsbase_read_task(task);

- if (doit)
- rdmsrl(MSR_KERNEL_GS_BASE, base);
- else
- base = task->thread.gsbase;
ret = put_user(base, (unsigned long __user *)arg2);
break;
}
diff --git a/arch/x86/kernel/ptrace.c b/arch/x86/kernel/ptrace.c
index fbde2a7ce377..d8f49c7384a3 100644
--- a/arch/x86/kernel/ptrace.c
+++ b/arch/x86/kernel/ptrace.c
@@ -397,12 +397,11 @@ static int putreg(struct task_struct *child,
if (value >= TASK_SIZE_MAX)
return -EIO;
/*
- * When changing the segment base, use do_arch_prctl_64
- * to set either thread.fs or thread.fsindex and the
- * corresponding GDT slot.
+ * When changing the FS base, use the same
+ * mechanism as for do_arch_prctl_64().
*/
if (child->thread.fsbase != value)
- return do_arch_prctl_64(child, ARCH_SET_FS, value);
+ return x86_fsbase_write_task(child, value);
return 0;
case offsetof(struct user_regs_struct,gs_base):
/*
@@ -411,7 +410,7 @@ static int putreg(struct task_struct *child,
if (value >= TASK_SIZE_MAX)
return -EIO;
if (child->thread.gsbase != value)
- return do_arch_prctl_64(child, ARCH_SET_GS, value);
+ return x86_gsbase_write_task(child, value);
return 0;
#endif
}
@@ -435,20 +434,10 @@ static unsigned long getreg(struct task_struct *task, unsigned long offset)
return get_flags(task);

#ifdef CONFIG_X86_64
- case offsetof(struct user_regs_struct, fs_base): {
- if (task->thread.fsindex == 0)
- return task->thread.fsbase;
- else
- 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 x86_fsgsbase_read_task(task,
- task->thread.gsindex);
- }
+ case offsetof(struct user_regs_struct, fs_base):
+ return x86_fsbase_read_task(task);
+ case offsetof(struct user_regs_struct, gs_base):
+ return x86_gsbase_read_task(task);
#endif
}