diff options
Diffstat (limited to 'arch/x86/entry/common.c')
| -rw-r--r-- | arch/x86/entry/common.c | 17 |
1 files changed, 15 insertions, 2 deletions
diff --git a/arch/x86/entry/common.c b/arch/x86/entry/common.c index 88dc5ba14d47..0ed023d6a983 100644 --- a/arch/x86/entry/common.c +++ b/arch/x86/entry/common.c @@ -363,7 +363,7 @@ __visible void do_int80_syscall_32(struct pt_regs *regs) syscall_return_slowpath(regs); } -/* Returns 0 to return using IRET or 1 to return using SYSRETL. */ +/* Returns 0 to return using IRET or 1 to return using SYSEXIT/SYSRETL. */ __visible long do_fast_syscall_32(struct pt_regs *regs) { /* @@ -417,7 +417,20 @@ __visible long do_fast_syscall_32(struct pt_regs *regs) regs->ip == landing_pad && (regs->flags & (X86_EFLAGS_RF | X86_EFLAGS_TF)) == 0; #else - return 0; + /* + * Opportunistic SYSEXIT: if possible, try to return using SYSEXIT. + * + * Unlike 64-bit opportunistic SYSRET, we can't check that CX == IP, + * because the ECX fixup above will ensure that this is essentially + * never the case. + * + * We don't allow syscalls at all from VM86 mode, but we still + * need to check VM, because we might be returning from sys_vm86. + */ + return static_cpu_has(X86_FEATURE_SEP) && + regs->cs == __USER_CS && regs->ss == __USER_DS && + regs->ip == landing_pad && + (regs->flags & (X86_EFLAGS_RF | X86_EFLAGS_TF | X86_EFLAGS_VM)) == 0; #endif } #endif |