2016-09-30 5:01 GMT+08:00 Andy Lutomirski <[email protected]>: > On Mon, Sep 26, 2016 at 4:49 AM, Wanpeng Li <[email protected]> wrote: >> From: Wanpeng Li <[email protected]> >> >> 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 <[email protected]> >> Cc: Ingo Molnar <[email protected]> >> Cc: "H. Peter Anvin" <[email protected]> >> Cc: Andy Lutomirski <[email protected]> >> Cc: Borislav Petkov <[email protected]> >> Signed-off-by: Wanpeng Li <[email protected]> >> --- >> 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. Regards, Wanpeng Li
