On Sep 29, 2016 5:43 PM, "Wanpeng Li" <kernel...@gmail.com> wrote: > > 2016-09-30 5:01 GMT+08:00 Andy Lutomirski <l...@amacapital.net>: > > On Mon, Sep 26, 2016 at 4:49 AM, Wanpeng Li <kernel...@gmail.com> wrote: > >> From: Wanpeng Li <wanpeng...@hotmail.com> > >> > >> WARNING: CPU: 0 PID: 3331 at arch/x86/entry/common.c:45 > >> enter_from_user_mode+0x32/0x50 > >> CPU: 0 PID: 3331 Comm: ldt_gdt_64 Not tainted 4.8.0-rc7+ #13 > >> Call Trace: > >> dump_stack+0x99/0xd0 > >> __warn+0xd1/0xf0 > >> warn_slowpath_null+0x1d/0x20 > >> enter_from_user_mode+0x32/0x50 > >> error_entry+0x6d/0xc0 > >> ? general_protection+0x12/0x30 > >> ? native_load_gs_index+0xd/0x20 > >> ? do_set_thread_area+0x19c/0x1f0 > >> SyS_set_thread_area+0x24/0x30 > >> do_int80_syscall_32+0x7c/0x220 > >> entry_INT80_compat+0x38/0x50 > >> > >> This can be reproduced by running the GS testcase of ldt_gdt test unit in > >> selftests. > >> > >> do_int80_syscall_32() will call enter_form_user_mode() to convert context > >> tracking state from user state to kernel state. The load_gs_index can fail > >> with user gsbase, gsbase will be fixed up and proceed if this happen. > >> However, enter_from_user_mode() will be called again in the fixed up path > >> though it is context tracking kernel state currently. > >> > >> This patch fix it by just fixing up gsbase and telling lockdep that IRQs > >> are off once load_gs_index failed with user gsbase. > >> > >> Cc: Thomas Gleixner <t...@linutronix.de> > >> Cc: Ingo Molnar <mi...@redhat.com> > >> Cc: "H. Peter Anvin" <h...@zytor.com> > >> Cc: Andy Lutomirski <l...@kernel.org> > >> Cc: Borislav Petkov <b...@alien8.de> > >> Signed-off-by: Wanpeng Li <wanpeng...@hotmail.com> > >> --- > >> arch/x86/entry/entry_64.S | 4 +++- > >> 1 file changed, 3 insertions(+), 1 deletion(-) > >> > >> diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S > >> index d172c61..dc1ec23 100644 > >> --- a/arch/x86/entry/entry_64.S > >> +++ b/arch/x86/entry/entry_64.S > >> @@ -1045,7 +1045,9 @@ ENTRY(error_entry) > >> * gsbase and proceed. We'll fix up the exception and land in > >> * .Lgs_change's error handler with kernel gsbase. > >> */ > >> - jmp .Lerror_entry_from_usermode_swapgs > >> + SWAPGS > >> + TRACE_IRQS_OFF > > > > Let's make this more readable: can you change this to: > > > > SWAPGS > > jmp .Lerror_entry_done > > > > and remove the .Lerror_entry_from_usermode_swapgs label as well? > > I will do this in v2. Btw, could you point out why the GS testcase in > tools/testing/selftests/x86/ldt_gdt.c will #GP? SDM said that swapgs > will #GP if CPL != 0, however, native_load_gs_index() is CPL == 0.
The fault is on MOV, not SWAPGS. --Andy
