Re: [PATCH 1/1] get_nr_restart_syscall() should return __NR_ia32_restart_syscall if __USER32_CS

Oleg Nesterov
2017-03-29T15:05:42Z

On 03/28, Oleg Nesterov wrote:
>
> On 03/28, Andy Lutomirski wrote:
> >
> > How about we store the syscall arch to be restored in task_struct
> > along with restart_block?
>
> Yes, perhaps we will have to finally do this. Not really nice too.

OK, how about the hack below?

I do not want to a new member into task_struct/restart_block, so the
patch below adds a sticky TS_COMPAT bit which logically is a member
of "struct restart_block".

TS_I386_REGS_POKED must die, I think. But this needs another discussion.

Oleg.

diff --git a/arch/x86/entry/common.c b/arch/x86/entry/common.c
index b83c61c..a94bb5e 100644
--- a/arch/x86/entry/common.c
+++ b/arch/x86/entry/common.c
@@ -249,6 +249,17 @@ __visible inline void syscall_return_slowpath(struct pt_regs *regs)
local_irq_enable();

/*
+ * Do this before debugger can change the regs.
+ */
+ if (IS_ENABLED(CONFIG_IA32_EMULATION) &&
+ unlikely(regs->ax == -ERESTART_RESTARTBLOCK)) {
+ if (current->thread.status & TS_COMPAT)
+ current->thread.status |= TS_COMPAT_XXX;
+ else
+ current->thread.status &= ~TS_COMPAT_XXX;
+ }
+
+ /*
* First do one-time work. If these work items are enabled, we
* want to run them exactly once per syscall exit with IRQs on.
*/
diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index 1be64da..87179ab 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -477,6 +477,7 @@ struct thread_struct {
* have to worry about atomic accesses.
*/
#define TS_COMPAT 0x0002 /* 32bit syscall active (64BIT)*/
+#define TS_COMPAT_XXX 0x0008

/*
* Set IOPL bits in EFLAGS from given mask
diff --git a/arch/x86/kernel/signal.c b/arch/x86/kernel/signal.c
index 763af1d..b3b98ff 100644
--- a/arch/x86/kernel/signal.c
+++ b/arch/x86/kernel/signal.c
@@ -785,7 +785,7 @@ static inline unsigned long get_nr_restart_syscall(const struct pt_regs *regs)
* than the tracee.
*/
#ifdef CONFIG_IA32_EMULATION
- if (current->thread.status & (TS_COMPAT|TS_I386_REGS_POKED))
+ if (current->thread.status & TS_COMPAT_XXX)
return __NR_ia32_restart_syscall;
#endif
#ifdef CONFIG_X86_X32_ABI