xen/pv: Fix a boot up hang revealed by int3 self test

Commit 7457c0da024b ("x86/alternatives: Add int3_emulate_call()
selftest") is used to ensure there is a gap setup in int3 exception stack
which could be used for inserting call return address.

This gap is missed in XEN PV int3 exception entry path, then below panic
triggered:

[    0.772876] general protection fault: 0000 [#1] SMP NOPTI
[    0.772886] CPU: 0 PID: 0 Comm: swapper/0 Not tainted 5.2.0+ #11
[    0.772893] RIP: e030:int3_magic+0x0/0x7
[    0.772905] RSP: 3507:ffffffff82203e98 EFLAGS: 00000246
[    0.773334] Call Trace:
[    0.773334]  alternative_instructions+0x3d/0x12e
[    0.773334]  check_bugs+0x7c9/0x887
[    0.773334]  ? __get_locked_pte+0x178/0x1f0
[    0.773334]  start_kernel+0x4ff/0x535
[    0.773334]  ? set_init_arg+0x55/0x55
[    0.773334]  xen_start_kernel+0x571/0x57a

For 64bit PV guests, Xen's ABI enters the kernel with using SYSRET, with
%rcx/%r11 on the stack. To convert back to "normal" looking exceptions,
the xen thunks do 'xen_*: pop %rcx; pop %r11; jmp *'.

E.g. Extracting 'xen_pv_trap xenint3' we have:
xen_xenint3:
 pop %rcx;
 pop %r11;
 jmp xenint3

As xenint3 and int3 entry code are same except xenint3 doesn't generate
a gap, we can fix it by using int3 and drop useless xenint3.

Signed-off-by: Zhenzhong Duan <zhenzhong.duan@oracle.com>
Reviewed-by: Juergen Gross <jgross@suse.com>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: Stefano Stabellini <sstabellini@kernel.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Andrew Cooper <andrew.cooper3@citrix.com>
Signed-off-by: Juergen Gross <jgross@suse.com>

diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index 0ea4831a72a47de6bf590685a0b7d474a3259c3b..35a66fcfcb91bed1a5a4315cb6204bae76c6aa98 100644 (file)
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -1176,7 +1176,6 @@ idtentry stack_segment            do_stack_segment        has_error_code=1
 #ifdef CONFIG_XEN_PV
 idtentry xennmi                        do_nmi                  has_error_code=0
 idtentry xendebug              do_debug                has_error_code=0
-idtentry xenint3               do_int3                 has_error_code=0
 #endif
 
 idtentry general_protection    do_general_protection   has_error_code=1

diff --git a/arch/x86/include/asm/traps.h b/arch/x86/include/asm/traps.h
index 7d6f3f3fad786916bfcfdb378d0a790ddaa54f5f..f2bd284abc16d848165b10221a7e28b1038d693c 100644 (file)
--- a/arch/x86/include/asm/traps.h
+++ b/arch/x86/include/asm/traps.h
@@ -40,7 +40,7 @@ asmlinkage void simd_coprocessor_error(void);
 asmlinkage void xen_divide_error(void);
 asmlinkage void xen_xennmi(void);
 asmlinkage void xen_xendebug(void);
-asmlinkage void xen_xenint3(void);
+asmlinkage void xen_int3(void);
 asmlinkage void xen_overflow(void);
 asmlinkage void xen_bounds(void);
 asmlinkage void xen_invalid_op(void);

diff --git a/arch/x86/xen/enlighten_pv.c b/arch/x86/xen/enlighten_pv.c
index 5d16824e4dca9542d035ee463e7209c1ecc561c9..bed6bb93c9652cfdc2bc9dbad64ad89ed2f72d2e 100644 (file)
--- a/arch/x86/xen/enlighten_pv.c
+++ b/arch/x86/xen/enlighten_pv.c
@@ -596,12 +596,12 @@ struct trap_array_entry {
 
 static struct trap_array_entry trap_array[] = {
        { debug,                       xen_xendebug,                    true },
-       { int3,                        xen_xenint3,                     true },
        { double_fault,                xen_double_fault,                true },
 #ifdef CONFIG_X86_MCE
        { machine_check,               xen_machine_check,               true },
 #endif
        { nmi,                         xen_xennmi,                      true },
+       { int3,                        xen_int3,                        false },
        { overflow,                    xen_overflow,                    false },
 #ifdef CONFIG_IA32_EMULATION
        { entry_INT80_compat,          xen_entry_INT80_compat,          false },

diff --git a/arch/x86/xen/xen-asm_64.S b/arch/x86/xen/xen-asm_64.S
index 1e9ef0ba30a582d841226708a695da6a098fb5fc..ebf610b49c0687e997d7ada1be17165c91edb5b2 100644 (file)
--- a/arch/x86/xen/xen-asm_64.S
+++ b/arch/x86/xen/xen-asm_64.S
@@ -32,7 +32,6 @@ xen_pv_trap divide_error
 xen_pv_trap debug
 xen_pv_trap xendebug
 xen_pv_trap int3
-xen_pv_trap xenint3
 xen_pv_trap xennmi
 xen_pv_trap overflow
 xen_pv_trap bounds