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Date: Wed, 29 Mar 2017 17:05:35 +0200 From: Oleg Nesterov <oleg@...hat.com> To: Andy Lutomirski <luto@...nel.org> Cc: Andrew Morton <akpm@...ux-foundation.org>, Linus Torvalds <torvalds@...ux-foundation.org>, Denys Vlasenko <dvlasenk@...hat.com>, "H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>, Jan Kratochvil <jan.kratochvil@...hat.com>, Pedro Alves <palves@...hat.com>, Thomas Gleixner <tglx@...utronix.de>, X86 ML <x86@...nel.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org> Subject: Re: [PATCH 1/1] get_nr_restart_syscall() should return __NR_ia32_restart_syscall if __USER32_CS 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
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