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From: "tip-bot2 for Lai Jiangshan" <tip-bot2@linutronix.de>
To: linux-tip-commits@vger.kernel.org
Cc: Lai Jiangshan <laijs@linux.alibaba.com>,
	Borislav Petkov <bp@suse.de>,
	Boris Ostrovsky <boris.ostrovsky@oracle.com>,
	x86@kernel.org, linux-kernel@vger.kernel.org
Subject: [tip: x86/urgent] x86/xen: Add xenpv_restore_regs_and_return_to_usermode()
Date: Sat, 04 Dec 2021 11:45:25 -0000	[thread overview]
Message-ID: <163861832551.11128.1645285137833652414.tip-bot2@tip-bot2> (raw)
In-Reply-To: <20211126101209.8613-4-jiangshanlai@gmail.com>

The following commit has been merged into the x86/urgent branch of tip:

Commit-ID:     5c8f6a2e316efebb3ba93d8c1af258155dcf5632
Gitweb:        https://git.kernel.org/tip/5c8f6a2e316efebb3ba93d8c1af258155dcf5632
Author:        Lai Jiangshan <laijs@linux.alibaba.com>
AuthorDate:    Fri, 26 Nov 2021 18:11:23 +08:00
Committer:     Borislav Petkov <bp@suse.de>
CommitterDate: Fri, 03 Dec 2021 19:21:15 +01:00

x86/xen: Add xenpv_restore_regs_and_return_to_usermode()

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.

In that case, source and destination stacks are identical, which means
that 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.

This is dangerous as it can 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, with  XEN pv, 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.

 [ bp: Massage commit message. ]

Fixes: 7f2590a110b8 ("x86/entry/64: Use a per-CPU trampoline stack for IDT entries")
Signed-off-by: Lai Jiangshan <laijs@linux.alibaba.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Link: https://lkml.kernel.org/r/20211126101209.8613-4-jiangshanlai@gmail.com
---
 arch/x86/entry/entry_64.S |  4 ++++
 arch/x86/xen/xen-asm.S    | 20 ++++++++++++++++++++
 2 files changed, 24 insertions(+)

diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index f9e1c06..97b1f84 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -574,6 +574,10 @@ SYM_INNER_LABEL(swapgs_restore_regs_and_return_to_usermode, SYM_L_GLOBAL)
 	ud2
 1:
 #endif
+#ifdef CONFIG_XEN_PV
+	ALTERNATIVE "", "jmp xenpv_restore_regs_and_return_to_usermode", X86_FEATURE_XENPV
+#endif
+
 	POP_REGS pop_rdi=0
 
 	/*
diff --git a/arch/x86/xen/xen-asm.S b/arch/x86/xen/xen-asm.S
index 220dd96..444d824 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"
 /*
@@ -193,6 +194,25 @@ SYM_CODE_START(xen_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
+	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:
  * - kernel gs

  reply	other threads:[~2021-12-04 11:45 UTC|newest]

Thread overview: 58+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-11-26 10:11 [PATCH V6 00/49] x86/entry/64: Convert a bunch of ASM entry code into C code Lai Jiangshan
2021-11-26 10:11 ` [PATCH V6 01/49] x86/entry: Add fence for kernel entry swapgs in paranoid_entry() Lai Jiangshan
2021-12-04 11:45   ` [tip: x86/urgent] x86/entry: Add a fence for kernel entry SWAPGS " tip-bot2 for Lai Jiangshan
2021-11-26 10:11 ` [PATCH V6 02/49] x86/entry: Use the correct fence macro after swapgs in kernel CR3 Lai Jiangshan
2021-12-04 11:45   ` [tip: x86/urgent] " tip-bot2 for Lai Jiangshan
2021-11-26 10:11 ` [PATCH V6 03/49] x86/xen: Add xenpv_restore_regs_and_return_to_usermode() Lai Jiangshan
2021-12-04 11:45   ` tip-bot2 for Lai Jiangshan [this message]
2021-11-26 10:11 ` [PATCH V6 04/49] x86/entry: Use swapgs and native_iret directly in swapgs_restore_regs_and_return_to_usermode Lai Jiangshan
2021-11-26 10:11 ` [PATCH V6 05/49] compiler_types.h: Add __noinstr_section() for noinstr Lai Jiangshan
2021-11-26 10:11 ` [PATCH V6 06/49] x86/entry: Introduce __entry_text for entry code written in C Lai Jiangshan
2021-11-26 10:11 ` [PATCH V6 07/49] x86/entry: Move PTI_USER_* to arch/x86/include/asm/processor-flags.h Lai Jiangshan
2021-11-26 10:11 ` [PATCH V6 08/49] x86: Remove unused kernel_to_user_p4dp() and user_to_kernel_p4dp() Lai Jiangshan
2021-11-26 10:11 ` [PATCH V6 09/49] x86: Replace PTI_PGTABLE_SWITCH_BIT with PTI_USER_PGTABLE_BIT Lai Jiangshan
2021-11-26 10:11 ` [PATCH V6 10/49] x86: Mark __native_read_cr3() & native_write_cr3() as __always_inline Lai Jiangshan
2021-11-26 10:11 ` [PATCH V6 11/49] x86/traps: Move the declaration of native_irq_return_iret into proto.h Lai Jiangshan
2021-11-26 10:11 ` [PATCH V6 12/49] x86/entry: Add arch/x86/entry/entry64.c for C entry code Lai Jiangshan
2021-11-26 10:11 ` [PATCH V6 13/49] x86/entry: Expose the address of .Lgs_change to entry64.c Lai Jiangshan
2021-11-26 10:11 ` [PATCH V6 14/49] x86/entry: Add C verion of SWITCH_TO_KERNEL_CR3 as switch_to_kernel_cr3() Lai Jiangshan
2021-11-26 10:11 ` [PATCH V6 15/49] x86/traps: Add fence_swapgs_{user,kernel}_entry() Lai Jiangshan
2021-11-26 10:11 ` [PATCH V6 16/49] x86/entry: Add C user_entry_swapgs_and_fence() Lai Jiangshan
2021-11-26 10:11 ` [PATCH V6 17/49] x86/traps: Move pt_regs only in fixup_bad_iret() Lai Jiangshan
2021-11-26 10:11 ` [PATCH V6 18/49] x86/entry: Switch the stack after error_entry() returns Lai Jiangshan
2021-11-26 10:11 ` [PATCH V6 19/49] x86/entry: move PUSH_AND_CLEAR_REGS out of error_entry Lai Jiangshan
2021-11-26 10:11 ` [PATCH V6 20/49] x86/entry: Move cld to the start of idtentry Lai Jiangshan
2021-11-26 10:11 ` [PATCH V6 21/49] x86/entry: Don't call error_entry for XENPV Lai Jiangshan
2021-11-26 10:11 ` [PATCH V6 22/49] x86/entry: Convert SWAPGS to swapgs in error_entry() Lai Jiangshan
2021-11-26 10:11 ` [PATCH V6 23/49] x86/entry: Implement the whole error_entry() as C code Lai Jiangshan
2021-11-26 10:11 ` [PATCH V6 24/49] x86/entry: Use idtentry macro for entry_INT80_compat Lai Jiangshan
2021-11-26 10:11 ` [PATCH V6 25/49] x86/entry: Convert SWAPGS to swapgs in entry_SYSENTER_compat() Lai Jiangshan
2021-11-26 10:11 ` [PATCH V6 26/49] x86: Remove the definition of SWAPGS Lai Jiangshan
2021-11-26 10:11 ` [PATCH V6 27/49] x86/entry: Make paranoid_exit() callable Lai Jiangshan
2021-11-26 10:11 ` [PATCH V6 28/49] x86/entry: Call paranoid_exit() in asm_exc_nmi() Lai Jiangshan
2021-11-26 10:11 ` [PATCH V6 29/49] x86/entry: move PUSH_AND_CLEAR_REGS out of paranoid_entry Lai Jiangshan
2021-11-26 10:11 ` [PATCH V6 30/49] x86/entry: Add the C version ist_switch_to_kernel_cr3() Lai Jiangshan
2021-11-26 10:11 ` [PATCH V6 31/49] x86/entry: Skip CR3 write when the saved CR3 is kernel CR3 in RESTORE_CR3 Lai Jiangshan
2021-11-26 10:11 ` [PATCH V6 32/49] x86/entry: Add the C version ist_restore_cr3() Lai Jiangshan
2021-11-26 10:11 ` [PATCH V6 33/49] x86/entry: Add the C version get_percpu_base() Lai Jiangshan
2021-11-26 10:11 ` [PATCH V6 34/49] x86/entry: Add the C version ist_switch_to_kernel_gsbase() Lai Jiangshan
2021-11-26 10:11 ` [PATCH V6 35/49] x86/entry: Implement the C version ist_paranoid_entry() Lai Jiangshan
2021-11-26 10:11 ` [PATCH V6 36/49] x86/entry: Implement the C version ist_paranoid_exit() Lai Jiangshan
2021-11-26 10:11 ` [PATCH V6 37/49] x86/entry: Add a C macro to define the function body for IST in .entry.text Lai Jiangshan
2021-11-26 10:11 ` [PATCH V6 38/49] x86/debug, mce: Use C entry code Lai Jiangshan
2021-11-26 10:11 ` [PATCH V6 39/49] x86/idtentry.h: Move the definitions *IDTENTRY_{MCE|DEBUG}* up Lai Jiangshan
2021-11-26 10:12 ` [PATCH V6 40/49] x86/nmi: Use DEFINE_IDTENTRY_NMI for nmi Lai Jiangshan
2021-11-26 10:12 ` [PATCH V6 41/49] x86/nmi: Use C entry code Lai Jiangshan
2021-11-26 10:12 ` [PATCH V6 42/49] x86/entry: Add a C macro to define the function body for IST in .entry.text with an error code Lai Jiangshan
2021-11-26 10:12 ` [PATCH V6 43/49] x86/doublefault: Use C entry code Lai Jiangshan
2021-11-26 10:12 ` [PATCH V6 44/49] x86/sev: Add and use ist_vc_switch_off_ist() Lai Jiangshan
2021-11-26 10:12 ` [PATCH V6 45/49] x86/sev: Use C entry code Lai Jiangshan
2021-11-26 10:12 ` [PATCH V6 46/49] x86/entry: Remove ASM function paranoid_entry() and paranoid_exit() Lai Jiangshan
2021-11-26 10:12 ` [PATCH V6 47/49] x86/entry: Remove the unused ASM macros Lai Jiangshan
2021-11-26 10:12 ` [PATCH V6 48/49] x86/entry: Remove save_ret from PUSH_AND_CLEAR_REGS Lai Jiangshan
2021-11-26 10:12 ` [PATCH V6 49/49] x86/syscall/64: Move the checking for sysret to C code Lai Jiangshan
2021-11-27 17:46 ` [PATCH V6 00/49] x86/entry/64: Convert a bunch of ASM entry code into " Damian Tometzki
2021-12-03  9:31 ` Lai Jiangshan
2021-12-03  9:39   ` Borislav Petkov
2021-12-03 10:10     ` Lai Jiangshan
2021-12-03 10:18       ` Borislav Petkov

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