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Date: Fri, 2 Jul 2010 19:05:19 -0600 From: Jeffrey Merkey <jeffmerkey@...il.com> To: linux-kernel@...r.kernel.org Subject: Re: 2.6.34 rex64 sysret instruction setup not preserving flags (r11 contents and eflags do not match) On Fri, Jul 2, 2010 at 4:18 PM, Jeffrey Merkey <jeffmerkey@...il.com> wrote: > On an AMD64 based system executing int 1 exceptions across a rex64 > sysret, if the debugger sets the trap flag, r11 which holds the eflags > values for the > sysret return from syscall, the flags do not appear to get set > resutling in the int exception nesting by calling sysret over and over > again until the kernel stack > runs off the end. Looks like the resume did not get set on this instruction. > > sysret on AMD requires the flags be saved into r11 and what I am > seeing is the flags not matching what has been set in the pt_regs > struct. > > Jeff > The specific function to look at is in entry_64.S sysret_check. The sequence goes; swapgs rex64 sysret After swapgs the eflags in r11 do not match the actual flags passed. The resume flag gets cleared when the sysret instruction completes, and int 1 keeps firing on that processor until the stack runs out of space. Jeff -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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