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Message-Id: <20211026141420.17138-5-jiangshanlai@gmail.com>
Date: Tue, 26 Oct 2021 22:13:34 +0800
From: Lai Jiangshan <jiangshanlai@...il.com>
To: linux-kernel@...r.kernel.org
Cc: x86@...nel.org, Lai Jiangshan <laijs@...ux.alibaba.com>,
Jan Beulich <jbeulich@...e.com>,
Thomas Gleixner <tglx@...utronix.de>,
Juergen Gross <jgross@...e.com>, Peter Anvin <hpa@...or.com>,
xen-devel@...ts.xenproject.org, Andy Lutomirski <luto@...nel.org>,
Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
Dave Hansen <dave.hansen@...ux.intel.com>,
Boris Ostrovsky <boris.ostrovsky@...cle.com>,
Stefano Stabellini <sstabellini@...nel.org>
Subject: [PATCH V4 04/50] x86/xen: Add xenpv_restore_regs_and_return_to_usermode()
From: Lai Jiangshan <laijs@...ux.alibaba.com>
While in the native case, PER_CPU_VAR(cpu_tss_rw + TSS_sp0) is the
trampoline stack. But XEN pv doesn't use trampoline stack, so
PER_CPU_VAR(cpu_tss_rw + TSS_sp0) is also the kernel stack. Hence source
and destination stacks are identical in that case, which means reusing
swapgs_restore_regs_and_return_to_usermode() in XEN pv would cause %rsp
to move up to the top of the kernel stack and leave the IRET frame below
%rsp, which is dangerous to be corrupted if #NMI / #MC hit as either of
these events occurring in the middle of the stack pushing would clobber
data on the (original) stack.
And swapgs_restore_regs_and_return_to_usermode() pushing the IRET frame
on to the original address is useless and error-prone when there is any
future attempt to modify the code.
Fixes: 7f2590a110b8 ("x86/entry/64: Use a per-CPU trampoline stack for IDT entries")
Cc: Jan Beulich <jbeulich@...e.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Juergen Gross <jgross@...e.com>
Cc: Peter Anvin <hpa@...or.com>
Cc: xen-devel@...ts.xenproject.org>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@...cle.com>
Signed-off-by: Lai Jiangshan <laijs@...ux.alibaba.com>
---
arch/x86/entry/entry_64.S | 9 ++++++---
arch/x86/entry/entry_64_compat.S | 7 ++++---
arch/x86/xen/xen-asm.S | 27 +++++++++++++++++++++++++++
3 files changed, 37 insertions(+), 6 deletions(-)
diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index 9d468c8877e2..0dde5a253dda 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -119,7 +119,7 @@ SYM_INNER_LABEL(entry_SYSCALL_64_after_hwframe, SYM_L_GLOBAL)
* In the Xen PV case we must use iret anyway.
*/
- ALTERNATIVE "", "jmp swapgs_restore_regs_and_return_to_usermode", \
+ ALTERNATIVE "", "jmp xenpv_restore_regs_and_return_to_usermode", \
X86_FEATURE_XENPV
movq RCX(%rsp), %rcx
@@ -286,7 +286,8 @@ SYM_CODE_START(ret_from_fork)
UNWIND_HINT_REGS
movq %rsp, %rdi
call syscall_exit_to_user_mode /* returns with IRQs disabled */
- jmp swapgs_restore_regs_and_return_to_usermode
+ ALTERNATIVE "jmp swapgs_restore_regs_and_return_to_usermode", \
+ "jmp xenpv_restore_regs_and_return_to_usermode", X86_FEATURE_XENPV
1:
/* kernel thread */
@@ -566,6 +567,7 @@ __irqentry_text_start:
__irqentry_text_end:
SYM_CODE_START_LOCAL(common_interrupt_return)
+SYM_INNER_LABEL(xenpv_restore_regs_and_return_to_usermode, SYM_L_WEAK) /* placeholder */
SYM_INNER_LABEL(swapgs_restore_regs_and_return_to_usermode, SYM_L_GLOBAL)
#ifdef CONFIG_DEBUG_ENTRY
/* Assert that pt_regs indicates user mode. */
@@ -1055,7 +1057,8 @@ SYM_CODE_START_LOCAL(error_return)
DEBUG_ENTRY_ASSERT_IRQS_OFF
testb $3, CS(%rsp)
jz restore_regs_and_return_to_kernel
- jmp swapgs_restore_regs_and_return_to_usermode
+ ALTERNATIVE "jmp swapgs_restore_regs_and_return_to_usermode", \
+ "jmp xenpv_restore_regs_and_return_to_usermode", X86_FEATURE_XENPV
SYM_CODE_END(error_return)
/*
diff --git a/arch/x86/entry/entry_64_compat.S b/arch/x86/entry/entry_64_compat.S
index 0051cf5c792d..2a4d9532dfd5 100644
--- a/arch/x86/entry/entry_64_compat.S
+++ b/arch/x86/entry/entry_64_compat.S
@@ -139,7 +139,7 @@ SYM_INNER_LABEL(entry_SYSENTER_compat_after_hwframe, SYM_L_GLOBAL)
call do_SYSENTER_32
/* XEN PV guests always use IRET path */
ALTERNATIVE "testl %eax, %eax; jz swapgs_restore_regs_and_return_to_usermode", \
- "jmp swapgs_restore_regs_and_return_to_usermode", X86_FEATURE_XENPV
+ "jmp xenpv_restore_regs_and_return_to_usermode", X86_FEATURE_XENPV
jmp sysret32_from_system_call
.Lsysenter_fix_flags:
@@ -256,7 +256,7 @@ SYM_INNER_LABEL(entry_SYSCALL_compat_after_hwframe, SYM_L_GLOBAL)
call do_fast_syscall_32
/* XEN PV guests always use IRET path */
ALTERNATIVE "testl %eax, %eax; jz swapgs_restore_regs_and_return_to_usermode", \
- "jmp swapgs_restore_regs_and_return_to_usermode", X86_FEATURE_XENPV
+ "jmp xenpv_restore_regs_and_return_to_usermode", X86_FEATURE_XENPV
/* Opportunistic SYSRET */
sysret32_from_system_call:
@@ -411,5 +411,6 @@ SYM_CODE_START(entry_INT80_compat)
movq %rsp, %rdi
call do_int80_syscall_32
- jmp swapgs_restore_regs_and_return_to_usermode
+ ALTERNATIVE "jmp swapgs_restore_regs_and_return_to_usermode", \
+ "jmp xenpv_restore_regs_and_return_to_usermode", X86_FEATURE_XENPV
SYM_CODE_END(entry_INT80_compat)
diff --git a/arch/x86/xen/xen-asm.S b/arch/x86/xen/xen-asm.S
index 220dd9678494..032be1bab113 100644
--- a/arch/x86/xen/xen-asm.S
+++ b/arch/x86/xen/xen-asm.S
@@ -20,6 +20,7 @@
#include <linux/init.h>
#include <linux/linkage.h>
+#include <../entry/calling.h>
.pushsection .noinstr.text, "ax"
/*
@@ -192,6 +193,32 @@ SYM_CODE_START(xen_iret)
jmp hypercall_iret
SYM_CODE_END(xen_iret)
+/*
+ * XEN pv doesn't use trampoline stack, PER_CPU_VAR(cpu_tss_rw + TSS_sp0) is
+ * also the kernel stack. Reusing swapgs_restore_regs_and_return_to_usermode()
+ * in XEN pv would cause %rsp to move up to the top of the kernel stack and
+ * leave the IRET frame below %rsp, which is dangerous to be corrupted if #NMI
+ * interrupts. And swapgs_restore_regs_and_return_to_usermode() pushing the IRET
+ * frame at the same address is useless.
+ */
+SYM_CODE_START(xenpv_restore_regs_and_return_to_usermode)
+ UNWIND_HINT_REGS
+#ifdef CONFIG_DEBUG_ENTRY
+ /* Assert that pt_regs indicates user mode. */
+ testb $3, CS(%rsp)
+ jnz 1f
+ ud2
+1:
+#endif
+ POP_REGS
+
+ /* stackleak_erase() can work safely on the kernel stack. */
+ STACKLEAK_ERASE_NOCLOBBER
+
+ addq $8, %rsp /* skip regs->orig_ax */
+ jmp xen_iret
+SYM_CODE_END(xenpv_restore_regs_and_return_to_usermode)
+
/*
* Xen handles syscall callbacks much like ordinary exceptions, which
* means we have:
--
2.19.1.6.gb485710b
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