* [Xen-devel] [PATCH v3] xen/pv: Fix a boot up hang revealed by int3 self test
@ 2019-07-14 9:15 Zhenzhong Duan
2019-07-17 4:46 ` Juergen Gross
2019-07-17 4:59 ` Juergen Gross
0 siblings, 2 replies; 3+ messages in thread
From: Zhenzhong Duan @ 2019-07-14 9:15 UTC (permalink / raw)
To: linux-kernel
Cc: jgross, sstabellini, Peter Zijlstra, Andrew Cooper, x86,
Zhenzhong Duan, mingo, bp, Andy Lutomirski, xen-devel,
boris.ostrovsky, tglx
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>
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>
---
bootup test pass with PV guest.
v3: set ist_okay to false for int3 per PeterZ
add Andrew's comments to patch description
v2: fix up description.
---
arch/x86/entry/entry_64.S | 1 -
arch/x86/include/asm/traps.h | 2 +-
arch/x86/xen/enlighten_pv.c | 2 +-
arch/x86/xen/xen-asm_64.S | 1 -
4 files changed, 2 insertions(+), 4 deletions(-)
diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index 0ea4831..35a66fc 100644
--- 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 7d6f3f3..f2bd284 100644
--- a/arch/x86/include/asm/traps.h
+++ b/arch/x86/include/asm/traps.h
@@ -40,7 +40,7 @@
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 4722ba2..30c14cb 100644
--- 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 1e9ef0b..ebf610b 100644
--- 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
--
1.8.3.1
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^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [Xen-devel] [PATCH v3] xen/pv: Fix a boot up hang revealed by int3 self test
2019-07-14 9:15 [Xen-devel] [PATCH v3] xen/pv: Fix a boot up hang revealed by int3 self test Zhenzhong Duan
@ 2019-07-17 4:46 ` Juergen Gross
2019-07-17 4:59 ` Juergen Gross
1 sibling, 0 replies; 3+ messages in thread
From: Juergen Gross @ 2019-07-17 4:46 UTC (permalink / raw)
To: Zhenzhong Duan, linux-kernel
Cc: sstabellini, Peter Zijlstra, Andrew Cooper, x86, mingo, bp,
Andy Lutomirski, xen-devel, tglx, boris.ostrovsky
On 14.07.19 11:15, Zhenzhong Duan wrote:
> 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>
Juergen
_______________________________________________
Xen-devel mailing list
Xen-devel@lists.xenproject.org
https://lists.xenproject.org/mailman/listinfo/xen-devel
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [Xen-devel] [PATCH v3] xen/pv: Fix a boot up hang revealed by int3 self test
2019-07-14 9:15 [Xen-devel] [PATCH v3] xen/pv: Fix a boot up hang revealed by int3 self test Zhenzhong Duan
2019-07-17 4:46 ` Juergen Gross
@ 2019-07-17 4:59 ` Juergen Gross
1 sibling, 0 replies; 3+ messages in thread
From: Juergen Gross @ 2019-07-17 4:59 UTC (permalink / raw)
To: Zhenzhong Duan, linux-kernel
Cc: sstabellini, Peter Zijlstra, Andrew Cooper, x86, mingo, bp,
Andy Lutomirski, xen-devel, tglx, boris.ostrovsky
On 14.07.19 11:15, Zhenzhong Duan wrote:
> 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>
Pushed to xen/tip.git for-linus-5.3a
Juergen
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Xen-devel mailing list
Xen-devel@lists.xenproject.org
https://lists.xenproject.org/mailman/listinfo/xen-devel
^ permalink raw reply [flat|nested] 3+ messages in thread
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2019-07-14 9:15 [Xen-devel] [PATCH v3] xen/pv: Fix a boot up hang revealed by int3 self test Zhenzhong Duan
2019-07-17 4:46 ` Juergen Gross
2019-07-17 4:59 ` Juergen Gross
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