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 <varad.gautam@xxxxxxxx>
---
lib/x86/desc.c | 28 ++++++++++++++++++++++------
lib/x86/desc.h | 1 +
2 files changed, 23 insertions(+), 6 deletions(-)
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);
--
2.32.0
