[kvm-unit-tests,v3,04/11] x86: desc: Split IDT entry setup into a generic helper

Commit Message

Varad Gautam April 26, 2022, 11:43 a.m. UTC

EFI bootstrapping code configures a call gate in a later commit to jump
from 16-bit to 32-bit code.

Introduce a set_desc_entry() routine which can be used to fill both
an interrupt descriptor and a call gate descriptor on x86.

Signed-off-by: Varad Gautam <[e-mail]>
---
 lib/x86/desc.c | 28 ++++++++++++++++++++++------
 lib/x86/desc.h |  1 +
 2 files changed, 23 insertions(+), 6 deletions(-)

Patch

diff --git a/lib/x86/desc.c b/lib/x86/desc.c
index 087e85c..a3e7255 100644
--- a/lib/x86/desc.c
+++ b/lib/x86/desc.c
@@ -57,22 +57,38 @@  __attribute__((regparm(1)))
 #endif
 void do_handle_exception(struct ex_regs *regs);
 
-void set_idt_entry(int vec, void *addr, int dpl)
+/*
+ * Fill an idt_entry_t, clearing e_sz bytes first.
+ *
+ * This can also be used to set up x86 call gates, since the gate
+ * descriptor layout is identical to idt_entry_t, except for the
+ * absence of .offset2 and .reserved fields. To do so, pass in e_sz
+ * according to the gate descriptor size.
+ */
+void set_desc_entry(idt_entry_t *e, size_t e_sz, void *addr,
+		u16 sel, u16 type, u16 dpl)
 {
-	idt_entry_t *e = &boot_idt[vec];
-	memset(e, 0, sizeof *e);
+	memset(e, 0, e_sz);
 	e->offset0 = (unsigned long)addr;
-	e->selector = read_cs();
+	e->selector = sel;
 	e->ist = 0;
-	e->type = 14;
+	e->type = type;
 	e->dpl = dpl;
 	e->p = 1;
 	e->offset1 = (unsigned long)addr >> 16;
 #ifdef __x86_64__
-	e->offset2 = (unsigned long)addr >> 32;
+	if (e_sz == sizeof(*e)) {
+		e->offset2 = (unsigned long)addr >> 32;
+	}
 #endif
 }
 
+void set_idt_entry(int vec, void *addr, int dpl)
+{
+	idt_entry_t *e = &boot_idt[vec];
+	set_desc_entry(e, sizeof *e, addr, read_cs(), 14, dpl);
+}
+
 void set_idt_dpl(int vec, u16 dpl)
 {
 	idt_entry_t *e = &boot_idt[vec];
diff --git a/lib/x86/desc.h b/lib/x86/desc.h
index 3044409..d743504 100644
--- a/lib/x86/desc.h
+++ b/lib/x86/desc.h
@@ -217,6 +217,7 @@  unsigned exception_vector(void);
 int write_cr4_checking(unsigned long val);
 unsigned exception_error_code(void);
 bool exception_rflags_rf(void);
+void set_desc_entry(idt_entry_t *e, size_t e_sz, void *addr, u16 sel, u16 type, u16 dpl);
 void set_idt_entry(int vec, void *addr, int dpl);
 void set_idt_sel(int vec, u16 sel);
 void set_idt_dpl(int vec, u16 dpl);