korg/linux
0
0
Fork 0
mirror of https://mirrors.bfsu.edu.cn/git/linux.git synced 2025-01-22 05:44:31 +08:00
Code Issues Packages Projects Releases Wiki Activity

x86/ptrace: Document FSBASE and GSBASE ABI oddities

Browse Source 
Signed-off-by: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Andy Lutomirski 2019-07-17 06:44:16 -07:00 committed by Ingo Molnar
parent 8e05f1b4f2
commit 56f2ab41b6
1 changed files with 17 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

17
arch/x86/kernel/ptrace.c
View File

@ -281,6 +281,20 @@ static int set_segment_reg(struct task_struct *task,
if (invalid_selector(value))
return -EIO;
/*
* This function has some ABI oddities.
*
* A 32-bit ptracer probably expects that writing FS or GS will change
* FSBASE or GSBASE respectively. In the absence of FSGSBASE support,
* this code indeed has that effect. When FSGSBASE is added, this
* will require a special case.
*
* For existing 64-bit ptracers, writing FS or GS *also* currently
* changes the base if the selector is nonzero the next time the task
* is run. This behavior may not be needed, and trying to preserve it
* when FSGSBASE is added would be complicated at best.
*/
switch (offset) {
case offsetof(struct user_regs_struct,fs):
task->thread.fsindex = value;
@ -370,6 +384,9 @@ static int putreg(struct task_struct *child,
* When changing the FS base, use do_arch_prctl_64()
* to set the index to zero and to set the base
* as requested.
*
* NB: This behavior is nonsensical and likely needs to
* change when FSGSBASE support is added.
*/
if (child->thread.fsbase != value)
return do_arch_prctl_64(child, ARCH_SET_FS, value);