On 7/30/23 23:41, Xin Li wrote:
+static DEFINE_FRED_HANDLER(fred_other_default)
+{
+ regs->vector = X86_TRAP_UD;
+ fred_emulate_fault(regs);
+}
+
+static DEFINE_FRED_HANDLER(fred_syscall)
+{
+ regs->orig_ax = regs->ax;
+ regs->ax = -ENOSYS;
+ do_syscall_64(regs, regs->orig_ax);
+}
+
+#if IS_ENABLED(CONFIG_IA32_EMULATION)
+/*
+ * Emulate SYSENTER if applicable. This is not the preferred system
+ * call in 32-bit mode under FRED, rather int $0x80 is preferred and
+ * exported in the vdso.
+ */
+static DEFINE_FRED_HANDLER(fred_sysenter)
+{
+ regs->orig_ax = regs->ax;
+ regs->ax = -ENOSYS;
+ do_fast_syscall_32(regs);
+}
+#else
+#define fred_sysenter fred_other_default
+#endif
+
+static DEFINE_FRED_HANDLER(fred_other)
+{
+ static const fred_handler user_other_handlers[FRED_NUM_OTHER_VECTORS] =
+ {
+ /*
+ * Vector 0 of the other event type is not used
+ * per FRED spec 5.0.
+ */
+ [0] = fred_other_default,
+ [FRED_SYSCALL] = fred_syscall,
+ [FRED_SYSENTER] = fred_sysenter
+ };
+
+ user_other_handlers[regs->vector](regs);
+}
OK, this is wrong.
Dispatching like fred_syscall() is only valid for syscall64, which means
you have to check regs->l is set in addition to the correct regs->vector
to determine validity.
Similarly, sysenter is only valid if regs->l is clear.
The best way is probably to drop the dispatch table here and just do an
if ... else if ... else statement; gcc is smart enough that it will
combine the vector test and the L bit test into a single mask and
compare. This also allows stubs to be inlined.
However, emulating #UD on events other than wrong mode of SYSCALL and
SYSENTER may be a bad idea. It would probably be better to invoke
fred_bad_event() in that case.
Something like this:
+static DEFINE_FRED_HANDLER(fred_other_default)
+{
+ regs->vector = X86_TRAP_UD;
+ fred_emulate_fault(regs);
+}
1) rename this to fred_emulate_ud (since that is what it actually does.)
... then ...
/* The compiler can fold these into a single test */
if (likely(regs->vector == FRED_SYSCALL && regs->l)) {
fred_syscall64(regs);
} else if (likely(regs->vector == FRED_SYSENTER && !regs->l)) {
fred_sysenter32(regs);
} else if (regs->vector == FRED_SYSCALL ||
regs->vector == FRED_SYSENTER) {
/* Invalid SYSCALL or SYSENTER instruction */
fred_emulate_ud(regs);
} else {
/* Unknown event */
fred_bad_event(regs);
}
... or the SYSCALL64 and SYSENTER32 can be inlined with the appropriate
comment (gcc will do so regardless.)
-hpa
-hpa
