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-rw-r--r--arch/x86/entry/common.c65
1 files changed, 65 insertions, 0 deletions
diff --git a/arch/x86/entry/common.c b/arch/x86/entry/common.c
index 6de50b80702e..51cc9c7cb9bd 100644
--- a/arch/x86/entry/common.c
+++ b/arch/x86/entry/common.c
@@ -255,6 +255,71 @@ __visible noinstr void do_int80_emulation(struct pt_regs *regs)
instrumentation_end();
syscall_exit_to_user_mode(regs);
}
+
+#ifdef CONFIG_X86_FRED
+/*
+ * A FRED-specific INT80 handler is warranted for the follwing reasons:
+ *
+ * 1) As INT instructions and hardware interrupts are separate event
+ * types, FRED does not preclude the use of vector 0x80 for external
+ * interrupts. As a result, the FRED setup code does not reserve
+ * vector 0x80 and calling int80_is_external() is not merely
+ * suboptimal but actively incorrect: it could cause a system call
+ * to be incorrectly ignored.
+ *
+ * 2) It is called only for handling vector 0x80 of event type
+ * EVENT_TYPE_SWINT and will never be called to handle any external
+ * interrupt (event type EVENT_TYPE_EXTINT).
+ *
+ * 3) FRED has separate entry flows depending on if the event came from
+ * user space or kernel space, and because the kernel does not use
+ * INT insns, the FRED kernel entry handler fred_entry_from_kernel()
+ * falls through to fred_bad_type() if the event type is
+ * EVENT_TYPE_SWINT, i.e., INT insns. So if the kernel is handling
+ * an INT insn, it can only be from a user level.
+ *
+ * 4) int80_emulation() does a CLEAR_BRANCH_HISTORY. While FRED will
+ * likely take a different approach if it is ever needed: it
+ * probably belongs in either fred_intx()/ fred_other() or
+ * asm_fred_entrypoint_user(), depending on if this ought to be done
+ * for all entries from userspace or only system
+ * calls.
+ *
+ * 5) INT $0x80 is the fast path for 32-bit system calls under FRED.
+ */
+DEFINE_FREDENTRY_RAW(int80_emulation)
+{
+ int nr;
+
+ enter_from_user_mode(regs);
+
+ instrumentation_begin();
+ add_random_kstack_offset();
+
+ /*
+ * FRED pushed 0 into regs::orig_ax and regs::ax contains the
+ * syscall number.
+ *
+ * User tracing code (ptrace or signal handlers) might assume
+ * that the regs::orig_ax contains a 32-bit number on invoking
+ * a 32-bit syscall.
+ *
+ * Establish the syscall convention by saving the 32bit truncated
+ * syscall number in regs::orig_ax and by invalidating regs::ax.
+ */
+ regs->orig_ax = regs->ax & GENMASK(31, 0);
+ regs->ax = -ENOSYS;
+
+ nr = syscall_32_enter(regs);
+
+ local_irq_enable();
+ nr = syscall_enter_from_user_mode_work(regs, nr);
+ do_syscall_32_irqs_on(regs, nr);
+
+ instrumentation_end();
+ syscall_exit_to_user_mode(regs);
+}
+#endif
#else /* CONFIG_IA32_EMULATION */
/* Handles int $0x80 on a 32bit kernel */