Am 20.08.2011 22:14, schrieb Al Viro: > On Sat, Aug 20, 2011 at 05:22:23PM +0200, Richard Weinberger wrote: > >> Hmmm, very strange. >> Sadly I cannot reproduce the issue. :( >> Everything works fine within UML. >> (Of course I've applied your vDSO/i386 patches) >> >> My test setup: >> Host kernel: 2.6.37 and 3.0.1 >> Distro: openSUSE 11.4/x86_64 >> >> UML kernel: 3.1-rc2 >> Distro: openSUSE 11.1/i386 >> >> Does the problem also occur with another host kernel or a different >> guest image? > > Could you check what you get in __kernel_vsyscall()? On iAMD64 box > where that sucker contains sysenter-based variant the bug is not > present. IOW, it's sensitive to syscall vs. systenter vs. int 0x80 > differences.
OK, this explains why I cannot reproduce it. My Intel Core2 box is sysenter-based. (gdb) disass __kernel_vsyscall 0xffffe420 <__kernel_vsyscall+0>: push %ecx 0xffffe421 <__kernel_vsyscall+1>: push %edx 0xffffe422 <__kernel_vsyscall+2>: push %ebp 0xffffe423 <__kernel_vsyscall+3>: mov %esp,%ebp 0xffffe425 <__kernel_vsyscall+5>: sysenter 0xffffe427 <__kernel_vsyscall+7>: nop 0xffffe428 <__kernel_vsyscall+8>: nop 0xffffe429 <__kernel_vsyscall+9>: nop 0xffffe42a <__kernel_vsyscall+10>: nop 0xffffe42b <__kernel_vsyscall+11>: nop 0xffffe42c <__kernel_vsyscall+12>: nop 0xffffe42d <__kernel_vsyscall+13>: nop 0xffffe42e <__kernel_vsyscall+14>: jmp 0xffffe423<__kernel_vsyscall+3> 0xffffe430 <__kernel_vsyscall+16>: pop %ebp 0xffffe431 <__kernel_vsyscall+17>: pop %edx 0xffffe432 <__kernel_vsyscall+18>: pop %ecx 0xffffe433 <__kernel_vsyscall+19>: ret > I can throw the trimmed-down fs image your way, BTW (66MB of bzipped ext2 ;-/) > if you want to see if that gets reproduced on your box. I'll drop it on > anonftp if you are interested. FWIW, the same kernel binary/same image > result in > * K7 box - no breakage, SYSENTER-based vdso > * K8 box - breakage as described, SYSCALL-based vdso32 > * P4 box - no breakage, SYSENTER-based vdso32 > Hell knows... In theory that would seem to point towards ia32_cstar_target(), > so I'm going to RTFS carefully through that animal. Now I'm testing with a Debian fs from: http://fs.devloop.org.uk/filesystems/Debian-Squeeze/ > The thing is, whatever happens happens when victim gets resumed inside > vdso page. I'll try to dump PTRACE_SETREGS and see the values host > kernel asked to set and work from there, but the interesting part is > bloody hard to singlestep through - the victim is back to user mode and > it is already traced by the guest kernel, so it's not as if we could > attach host gdb to it and walk through that crap. And guest gdb is not > going to be able to set breakpoints in there - vdso page is r/o... [ CC'ing l...@mit.edu ] Andy, do you have an idea? You can find Al's original report here: http://marc.info/?l=linux-kernel&m=131380315624244&w=2 Thanks, //richard ------------------------------------------------------------------------------ Get a FREE DOWNLOAD! and learn more about uberSVN rich system, user administration capabilities and model configuration. Take the hassle out of deploying and managing Subversion and the tools developers use with it. http://p.sf.net/sfu/wandisco-d2d-2 _______________________________________________ User-mode-linux-devel mailing list User-mode-linux-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/user-mode-linux-devel
