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

[ Upstream commit b23e5844dfe78a80ba672793187d3f52e4b528d7 ]

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>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index e09ba4bc8b98faa1c5fb3ed75895ba35982d78ad..b2524d349595c26ef8be227c7cf081dc700282df 100644 (file)
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -1113,7 +1113,6 @@ idtentry stack_segment            do_stack_segment        has_error_code=1
 #ifdef CONFIG_XEN
 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 afbc87206886e76d73995fe4be47c3568485ea76..b771bb3d159bc8ce27f7897a01f3af4d8be2a78a 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 481d7920ea244181c16822cacc5c57d15c7cd34b..f79a0cdc6b4e7ba23100a40447d981a89c929a02 100644 (file)
--- a/arch/x86/xen/enlighten_pv.c
+++ b/arch/x86/xen/enlighten_pv.c
@@ -598,12 +598,12 @@ 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 417b339e5c8e1aadedd20231c9be82ac93dbe728..3a6feed76dfc167736984315390e9b8b0cb81e6c 100644 (file)
--- a/arch/x86/xen/xen-asm_64.S
+++ b/arch/x86/xen/xen-asm_64.S
@@ -30,7 +30,6 @@ 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