diff options
Diffstat (limited to 'pkg/sentry/platform/ring0/x86.go')
| -rw-r--r-- | pkg/sentry/platform/ring0/x86.go | 38 |
1 files changed, 35 insertions, 3 deletions
diff --git a/pkg/sentry/platform/ring0/x86.go b/pkg/sentry/platform/ring0/x86.go index e99da0b35..34fbc1c35 100644 --- a/pkg/sentry/platform/ring0/x86.go +++ b/pkg/sentry/platform/ring0/x86.go @@ -39,7 +39,9 @@ const ( _RFLAGS_AC = 1 << 18 _RFLAGS_NT = 1 << 14 - _RFLAGS_IOPL = 3 << 12 + _RFLAGS_IOPL0 = 1 << 12 + _RFLAGS_IOPL1 = 1 << 13 + _RFLAGS_IOPL = _RFLAGS_IOPL0 | _RFLAGS_IOPL1 _RFLAGS_DF = 1 << 10 _RFLAGS_IF = 1 << 9 _RFLAGS_STEP = 1 << 8 @@ -67,15 +69,45 @@ const ( KernelFlagsSet = _RFLAGS_RESERVED // UserFlagsSet are always set in userspace. - UserFlagsSet = _RFLAGS_RESERVED | _RFLAGS_IF + // + // _RFLAGS_IOPL is a set of two bits and it shows the I/O privilege + // level. The Current Privilege Level (CPL) of the task must be less + // than or equal to the IOPL in order for the task or program to access + // I/O ports. + // + // Here, _RFLAGS_IOPL0 is used only to determine whether the task is + // running in the kernel or userspace mode. In the user mode, the CPL is + // always 3 and it doesn't matter what IOPL is set if it is bellow CPL. + // + // We need to have one bit which will be always different in user and + // kernel modes. And we have to remember that even though we have + // KernelFlagsClear, we still can see some of these flags in the kernel + // mode. This can happen when the goruntime switches on a goroutine + // which has been saved in the host mode. On restore, the popf + // instruction is used to restore flags and this means that all flags + // what the goroutine has in the host mode will be restored in the + // kernel mode. + // + // _RFLAGS_IOPL0 is never set in host and kernel modes and we always set + // it in the user mode. So if this flag is set, the task is running in + // the user mode and if it isn't set, the task is running in the kernel + // mode. + UserFlagsSet = _RFLAGS_RESERVED | _RFLAGS_IF | _RFLAGS_IOPL0 // KernelFlagsClear should always be clear in the kernel. KernelFlagsClear = _RFLAGS_STEP | _RFLAGS_IF | _RFLAGS_IOPL | _RFLAGS_AC | _RFLAGS_NT // UserFlagsClear are always cleared in userspace. - UserFlagsClear = _RFLAGS_NT | _RFLAGS_IOPL + UserFlagsClear = _RFLAGS_NT | _RFLAGS_IOPL1 ) +// IsKernelFlags returns true if rflags coresponds to the kernel mode. +// +// go:nosplit +func IsKernelFlags(rflags uint64) bool { + return rflags&_RFLAGS_IOPL0 == 0 +} + // Vector is an exception vector. type Vector uintptr |