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x86/sev: Mark the code returning to user space as syscall gap

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

If it is a SNP-guest and the hypervisor decides to mess with the
code-page for this path while a CPU is executing it, a potential #VC
could hit in the syscall return path and mislead the #VC handler.

So make ip_within_syscall_gap() return true in this case.

Signed-off-by: Lai Jiangshan <jiangshan.ljs@antgroup.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Acked-by: Joerg Roedel <jroedel@suse.de>
Link: https://lore.kernel.org/r/20220412124909.10467-1-jiangshanlai@gmail.com
This commit is contained in:
Lai Jiangshan 2022-04-12 20:49:08 +08:00 committed by Borislav Petkov
parent c42b145181
commit 47f33de4aa
4 changed files with 12 additions and 0 deletions
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2
arch/x86/entry/entry_64.S
View File

@ -215,8 +215,10 @@ 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)
/*

2
arch/x86/entry/entry_64_compat.S
View File

@ -297,6 +297,7 @@ 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
@ -314,6 +315,7 @@ 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)
/*

4
arch/x86/include/asm/proto.h
View File

@ -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);

4
arch/x86/include/asm/ptrace.h
View File

@ -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;