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Date: Wed, 19 Feb 2020 16:57:15 +0100 From: Peter Zijlstra <peterz@...radead.org> To: Steven Rostedt <rostedt@...dmis.org> Cc: linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org, mingo@...nel.org, joel@...lfernandes.org, gregkh@...uxfoundation.org, gustavo@...eddedor.com, tglx@...utronix.de, paulmck@...nel.org, josh@...htriplett.org, mathieu.desnoyers@...icios.com, jiangshanlai@...il.com, luto@...nel.org, tony.luck@...el.com, frederic@...nel.org, dan.carpenter@...cle.com, mhiramat@...nel.org Subject: Re: [PATCH v3 04/22] x86/doublefault: Make memmove() notrace/NOKPROBE On Wed, Feb 19, 2020 at 04:40:31PM +0100, Peter Zijlstra wrote: > On Wed, Feb 19, 2020 at 10:36:14AM -0500, Steven Rostedt wrote: > > On Wed, 19 Feb 2020 15:47:28 +0100 > > Peter Zijlstra <peterz@...radead.org> wrote: > > > > > --- a/arch/x86/lib/memcpy_32.c > > > +++ b/arch/x86/lib/memcpy_32.c > > > @@ -21,7 +21,7 @@ __visible void *memset(void *s, int c, s > > > } > > > EXPORT_SYMBOL(memset); > > > > > > -__visible void *memmove(void *dest, const void *src, size_t n) > > > +__visible notrace void *memmove(void *dest, const void *src, size_t n) > > > { > > > int d0,d1,d2,d3,d4,d5; > > > char *ret = dest; > > > @@ -207,3 +207,8 @@ __visible void *memmove(void *dest, cons > > > > > > } > > > EXPORT_SYMBOL(memmove); > > > > Hmm, for things like this, which is adding notrace because of a single > > instance of it (although it is fine to trace in any other instance), it > > would be nice to have a gcc helper that could call "memmove+5" which > > would skip the tracing portion. > > Or just open-code the memmove() in do_double_fault() I suppose. I don't > think we care about super optimized code there. It's the bloody ESPFIX > trainwreck. Something like so, I suppose... diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c index 6ef00eb6fbb9..543de932dc7c 100644 --- a/arch/x86/kernel/traps.c +++ b/arch/x86/kernel/traps.c @@ -350,14 +350,20 @@ dotraplinkage void do_double_fault(struct pt_regs *regs, long error_code, unsign regs->ip == (unsigned long)native_irq_return_iret) { struct pt_regs *gpregs = (struct pt_regs *)this_cpu_read(cpu_tss_rw.x86_tss.sp0) - 1; + unsigned long *dst = &gpregs->ip; + unsigned long *src = (void *)regs->dp; + int i, count = 5; /* * regs->sp points to the failing IRET frame on the * ESPFIX64 stack. Copy it to the entry stack. This fills * in gpregs->ss through gpregs->ip. - * */ - memmove(&gpregs->ip, (void *)regs->sp, 5*8); + for (i = 0; i < count; i++) { + int idx = (dst <= src) ? i : count - i; + dst[idx] = src[idx]; + } + gpregs->orig_ax = 0; /* Missing (lost) #GP error code */ /*
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