linux-kernel - [PATCH 3/3] x86/sev: The code for returning to user space is also in syscall gap

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Message-Id: <20211213042215.3096-4-jiangshanlai@gmail.com>
Date:   Mon, 13 Dec 2021 12:22:15 +0800
From:   Lai Jiangshan <jiangshanlai@...il.com>
To:     linux-kernel@...r.kernel.org
Cc:     x86@...nel.org, Lai Jiangshan <laijs@...ux.alibaba.com>,
        Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>, Oleg Nesterov <oleg@...hat.com>,
        "Chang S. Bae" <chang.seok.bae@...el.com>,
        Jan Kiszka <jan.kiszka@...mens.com>,
        Joerg Roedel <jroedel@...e.de>
Subject: [PATCH 3/3] x86/sev: The code for returning to user space is also in syscall gap

From: Lai Jiangshan <laijs@...ux.alibaba.com>

When returning to user space, the %rsp is user controlled value.

Signed-off-by: Lai Jiangshan <laijs@...ux.alibaba.com>
---
 arch/x86/entry/entry_64.S        | 2 ++
 arch/x86/entry/entry_64_compat.S | 2 ++
 arch/x86/include/asm/proto.h     | 4 ++++
 arch/x86/include/asm/ptrace.h    | 4 ++++
 4 files changed, 12 insertions(+)

diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index e23319ad3f42..44dadea935f7 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -213,8 +213,10 @@ syscall_return_via_sysret:
 
 	popq	%rdi
 	popq	%rsp
+SYM_INNER_LABEL(entry_SYSRETQ_unsafe_stack, SYM_L_GLOBAL)
 	swapgs
 	sysretq
+SYM_INNER_LABEL(entry_SYSRETQ_end, SYM_L_GLOBAL)
 SYM_CODE_END(entry_SYSCALL_64)
 
 /*
diff --git a/arch/x86/entry/entry_64_compat.S b/arch/x86/entry/entry_64_compat.S
index 0051cf5c792d..98afdf92f360 100644
--- a/arch/x86/entry/entry_64_compat.S
+++ b/arch/x86/entry/entry_64_compat.S
@@ -293,6 +293,7 @@ sysret32_from_system_call:
 	 * code.  We zero R8-R10 to avoid info leaks.
          */
 	movq	RSP-ORIG_RAX(%rsp), %rsp
+SYM_INNER_LABEL(entry_SYSRETL_compat_unsafe_stack, SYM_L_GLOBAL)
 
 	/*
 	 * The original userspace %rsp (RSP-ORIG_RAX(%rsp)) is stored
@@ -310,6 +311,7 @@ sysret32_from_system_call:
 	xorl	%r10d, %r10d
 	swapgs
 	sysretl
+SYM_INNER_LABEL(entry_SYSRETL_compat_end, SYM_L_GLOBAL)
 SYM_CODE_END(entry_SYSCALL_compat)
 
 /*
diff --git a/arch/x86/include/asm/proto.h b/arch/x86/include/asm/proto.h
index feed36d44d04..f042cfc9938f 100644
--- a/arch/x86/include/asm/proto.h
+++ b/arch/x86/include/asm/proto.h
@@ -13,6 +13,8 @@ void syscall_init(void);
 #ifdef CONFIG_X86_64
 void entry_SYSCALL_64(void);
 void entry_SYSCALL_64_safe_stack(void);
+void entry_SYSRETQ_unsafe_stack(void);
+void entry_SYSRETQ_end(void);
 long do_arch_prctl_64(struct task_struct *task, int option, unsigned long arg2);
 #endif
 
@@ -28,6 +30,8 @@ void entry_SYSENTER_compat(void);
 void __end_entry_SYSENTER_compat(void);
 void entry_SYSCALL_compat(void);
 void entry_SYSCALL_compat_safe_stack(void);
+void entry_SYSRETL_compat_unsafe_stack(void);
+void entry_SYSRETL_compat_end(void);
 void entry_INT80_compat(void);
 #ifdef CONFIG_XEN_PV
 void xen_entry_INT80_compat(void);
diff --git a/arch/x86/include/asm/ptrace.h b/arch/x86/include/asm/ptrace.h
index 703663175a5a..b3d2ba13cee2 100644
--- a/arch/x86/include/asm/ptrace.h
+++ b/arch/x86/include/asm/ptrace.h
@@ -186,9 +186,13 @@ static __always_inline bool ip_within_syscall_gap(struct pt_regs *regs)
 	bool ret = (regs->ip >= (unsigned long)entry_SYSCALL_64 &&
 		    regs->ip <  (unsigned long)entry_SYSCALL_64_safe_stack);
 
+	ret = ret || (regs->ip >= (unsigned long)entry_SYSRETQ_unsafe_stack &&
+		      regs->ip <  (unsigned long)entry_SYSRETQ_end);
 #ifdef CONFIG_IA32_EMULATION
 	ret = ret || (regs->ip >= (unsigned long)entry_SYSCALL_compat &&
 		      regs->ip <  (unsigned long)entry_SYSCALL_compat_safe_stack);
+	ret = ret || (regs->ip >= (unsigned long)entry_SYSRETL_compat_unsafe_stack &&
+		      regs->ip <  (unsigned long)entry_SYSRETL_compat_end);
 #endif
 
 	return ret;
-- 
2.19.1.6.gb485710b