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

Lai Jiangshan
2021-12-13T04:22:40Z

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

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

Signed-off-by: Lai Jiangshan <laijs@linux.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