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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [PATCH 13/16] x86/ioemul: Rewrite stub generation to be shadow stack compatible
The logic is completely undocumented and almost impossible to follow. It
actually uses return oriented programming. Rewrite it to conform to more
normal call mechanics, and leave a big comment explaining thing. As well as
the code being easier to follow, it will execute faster as it isn't fighting
the branch predictor.
Move the ioemul_handle_quirk() function pointer from traps.c to
ioport_emulate.c. There is no reason for it to be in neither of the two
translation units which use it. Alter the behaviour to return the number of
bytes written into the stub.
Access the addresses of the host/guest helpers with extern const char arrays.
Nothing good will come of C thinking they are regular functions.
Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
--
CC: Jan Beulich <JBeulich@xxxxxxxx>
CC: Wei Liu <wl@xxxxxxx>
CC: Roger Pau Monné <roger.pau@xxxxxxxxxx>
Posted previously on its perf benefits alone, but here is the real reason
behind the change.
---
xen/arch/x86/ioport_emulate.c | 11 ++---
xen/arch/x86/pv/emul-priv-op.c | 91 +++++++++++++++++++++++++++++++-----------
xen/arch/x86/pv/gpr_switch.S | 37 +++++------------
xen/arch/x86/traps.c | 3 --
xen/include/asm-x86/io.h | 3 +-
5 files changed, 85 insertions(+), 60 deletions(-)
diff --git a/xen/arch/x86/ioport_emulate.c b/xen/arch/x86/ioport_emulate.c
index 499c1f6056..f7511a9c49 100644
--- a/xen/arch/x86/ioport_emulate.c
+++ b/xen/arch/x86/ioport_emulate.c
@@ -8,7 +8,10 @@
#include <xen/sched.h>
#include <xen/dmi.h>
-static bool ioemul_handle_proliant_quirk(
+unsigned int (*ioemul_handle_quirk)(
+ u8 opcode, char *io_emul_stub, struct cpu_user_regs *regs);
+
+static unsigned int ioemul_handle_proliant_quirk(
u8 opcode, char *io_emul_stub, struct cpu_user_regs *regs)
{
static const char stub[] = {
@@ -19,18 +22,16 @@ static bool ioemul_handle_proliant_quirk(
0xa8, 0x80, /* test $0x80, %al */
0x75, 0xfb, /* jnz 1b */
0x9d, /* popf */
- 0xc3, /* ret */
};
uint16_t port = regs->dx;
uint8_t value = regs->al;
if ( (opcode != 0xee) || (port != 0xcd4) || !(value & 0x80) )
- return false;
+ return 0;
memcpy(io_emul_stub, stub, sizeof(stub));
- BUILD_BUG_ON(IOEMUL_QUIRK_STUB_BYTES < sizeof(stub));
- return true;
+ return sizeof(stub);
}
/* This table is the set of system-specific I/O emulation hooks. */
diff --git a/xen/arch/x86/pv/emul-priv-op.c b/xen/arch/x86/pv/emul-priv-op.c
index e24b84f46a..f150886711 100644
--- a/xen/arch/x86/pv/emul-priv-op.c
+++ b/xen/arch/x86/pv/emul-priv-op.c
@@ -54,51 +54,96 @@ struct priv_op_ctxt {
unsigned int bpmatch;
};
-/* I/O emulation support. Helper routines for, and type of, the stack stub. */
-void host_to_guest_gpr_switch(struct cpu_user_regs *);
-unsigned long guest_to_host_gpr_switch(unsigned long);
+/* I/O emulation helpers. Use non-standard calling conventions. */
+extern const char load_guest_gprs[], save_guest_gprs[];
typedef void io_emul_stub_t(struct cpu_user_regs *);
static io_emul_stub_t *io_emul_stub_setup(struct priv_op_ctxt *ctxt, u8 opcode,
unsigned int port, unsigned int
bytes)
{
+ /*
+ * Construct a stub for IN/OUT emulation.
+ *
+ * Some platform drivers communicate with the SMM handler using GPRs as a
+ * mailbox. Therefore, we must perform the emulation with the hardware
+ * domain's registers in view.
+ *
+ * We write a stub of the following form, using the guest load/save
+ * helpers (abnormal calling conventions), and one of several possible
+ * stubs performing the real I/O.
+ */
+ static const char prologue[] = {
+ 0x53, /* push %rbx */
+ 0x55, /* push %rbp */
+ 0x41, 0x54, /* push %r12 */
+ 0x41, 0x55, /* push %r13 */
+ 0x41, 0x56, /* push %r14 */
+ 0x41, 0x57, /* push %r15 */
+ 0x57, /* push %rdi (param for save_guest_gprs) */
+ }; /* call load_guest_gprs */
+ /* <I/O stub> */
+ /* call save_guest_gprs */
+ static const char epilogue[] = {
+ 0x5f, /* pop %rdi */
+ 0x41, 0x5f, /* pop %r15 */
+ 0x41, 0x5e, /* pop %r14 */
+ 0x41, 0x5d, /* pop %r13 */
+ 0x41, 0x5c, /* pop %r12 */
+ 0x5d, /* pop %rbp */
+ 0x5b, /* pop %rbx */
+ 0xc3, /* ret */
+ };
+
struct stubs *this_stubs = &this_cpu(stubs);
unsigned long stub_va = this_stubs->addr + STUB_BUF_SIZE / 2;
- long disp;
- bool use_quirk_stub = false;
+ unsigned int quirk_bytes = 0;
+ char *p;
+
+ /* Helpers - Read outer scope but only modify p. */
+#define APPEND_BUFF(b) ({ memcpy(p, b, sizeof(b)); p += sizeof(b); })
+#define APPEND_CALL(f) \
+ ({ \
+ long disp = (long)(f) - (stub_va + p - ctxt->io_emul_stub + 5); \
+ BUG_ON((int32_t)disp != disp); \
+ *p++ = 0xe8; \
+ *(int32_t *)p = disp; p += 4; \
+ })
if ( !ctxt->io_emul_stub )
ctxt->io_emul_stub =
map_domain_page(_mfn(this_stubs->mfn)) + (stub_va & ~PAGE_MASK);
- /* call host_to_guest_gpr_switch */
- ctxt->io_emul_stub[0] = 0xe8;
- disp = (long)host_to_guest_gpr_switch - (stub_va + 5);
- BUG_ON((int32_t)disp != disp);
- *(int32_t *)&ctxt->io_emul_stub[1] = disp;
+ p = ctxt->io_emul_stub;
+
+ APPEND_BUFF(prologue);
+ APPEND_CALL(load_guest_gprs);
+ /* Some platforms might need to quirk the stub for specific inputs. */
if ( unlikely(ioemul_handle_quirk) )
- use_quirk_stub = ioemul_handle_quirk(opcode, &ctxt->io_emul_stub[5],
- ctxt->ctxt.regs);
+ {
+ quirk_bytes = ioemul_handle_quirk(opcode, p, ctxt->ctxt.regs);
+ p += quirk_bytes;
+ }
- if ( !use_quirk_stub )
+ /* Default I/O stub. */
+ if ( likely(!quirk_bytes) )
{
- /* data16 or nop */
- ctxt->io_emul_stub[5] = (bytes != 2) ? 0x90 : 0x66;
- /* <io-access opcode> */
- ctxt->io_emul_stub[6] = opcode;
- /* imm8 or nop */
- ctxt->io_emul_stub[7] = !(opcode & 8) ? port : 0x90;
- /* ret (jumps to guest_to_host_gpr_switch) */
- ctxt->io_emul_stub[8] = 0xc3;
+ *p++ = (bytes != 2) ? 0x90 : 0x66; /* data16 or nop */
+ *p++ = opcode; /* <opcode> */
+ *p++ = !(opcode & 8) ? port : 0x90; /* imm8 or nop */
}
- BUILD_BUG_ON(STUB_BUF_SIZE / 2 < MAX(9, /* Default emul stub */
- 5 + IOEMUL_QUIRK_STUB_BYTES));
+ APPEND_CALL(save_guest_gprs);
+ APPEND_BUFF(epilogue);
+
+ BUG_ON(STUB_BUF_SIZE / 2 < (p - ctxt->io_emul_stub));
/* Handy function-typed pointer to the stub. */
return (void *)stub_va;
+
+#undef APPEND_CALL
+#undef APPEND_BUFF
}
diff --git a/xen/arch/x86/pv/gpr_switch.S b/xen/arch/x86/pv/gpr_switch.S
index 6d26192c2c..e3f8037b69 100644
--- a/xen/arch/x86/pv/gpr_switch.S
+++ b/xen/arch/x86/pv/gpr_switch.S
@@ -9,59 +9,42 @@
#include <asm/asm_defns.h>
-ENTRY(host_to_guest_gpr_switch)
- movq (%rsp), %rcx
- movq %rdi, (%rsp)
+/* Load guest GPRs. Parameter in %rdi, clobbers all registers. */
+ENTRY(load_guest_gprs)
movq UREGS_rdx(%rdi), %rdx
- pushq %rbx
movq UREGS_rax(%rdi), %rax
movq UREGS_rbx(%rdi), %rbx
- pushq %rbp
movq UREGS_rsi(%rdi), %rsi
movq UREGS_rbp(%rdi), %rbp
- pushq %r12
- movq UREGS_r8(%rdi), %r8
+ movq UREGS_r8 (%rdi), %r8
movq UREGS_r12(%rdi), %r12
- pushq %r13
- movq UREGS_r9(%rdi), %r9
+ movq UREGS_r9 (%rdi), %r9
movq UREGS_r13(%rdi), %r13
- pushq %r14
movq UREGS_r10(%rdi), %r10
movq UREGS_r14(%rdi), %r14
- pushq %r15
movq UREGS_r11(%rdi), %r11
movq UREGS_r15(%rdi), %r15
- pushq %rcx /* dummy push, filled by guest_to_host_gpr_switch pointer */
- pushq %rcx
- leaq guest_to_host_gpr_switch(%rip),%rcx
- movq %rcx,8(%rsp)
movq UREGS_rcx(%rdi), %rcx
movq UREGS_rdi(%rdi), %rdi
ret
-ENTRY(guest_to_host_gpr_switch)
+/* Save guest GPRs. Parameter on the stack above the return address. */
+ENTRY(save_guest_gprs)
pushq %rdi
- movq 7*8(%rsp), %rdi
+ movq 2*8(%rsp), %rdi
movq %rax, UREGS_rax(%rdi)
- popq UREGS_rdi(%rdi)
+ popq UREGS_rdi(%rdi)
movq %r15, UREGS_r15(%rdi)
movq %r11, UREGS_r11(%rdi)
- popq %r15
movq %r14, UREGS_r14(%rdi)
movq %r10, UREGS_r10(%rdi)
- popq %r14
movq %r13, UREGS_r13(%rdi)
- movq %r9, UREGS_r9(%rdi)
- popq %r13
+ movq %r9, UREGS_r9 (%rdi)
movq %r12, UREGS_r12(%rdi)
- movq %r8, UREGS_r8(%rdi)
- popq %r12
+ movq %r8, UREGS_r8 (%rdi)
movq %rbp, UREGS_rbp(%rdi)
movq %rsi, UREGS_rsi(%rdi)
- popq %rbp
movq %rbx, UREGS_rbx(%rdi)
movq %rdx, UREGS_rdx(%rdi)
- popq %rbx
movq %rcx, UREGS_rcx(%rdi)
- popq %rcx
ret
diff --git a/xen/arch/x86/traps.c b/xen/arch/x86/traps.c
index 2354357cc1..3923950df7 100644
--- a/xen/arch/x86/traps.c
+++ b/xen/arch/x86/traps.c
@@ -117,9 +117,6 @@ idt_entry_t *idt_tables[NR_CPUS] __read_mostly;
*/
DEFINE_PER_CPU_PAGE_ALIGNED(struct tss_page, tss_page);
-bool (*ioemul_handle_quirk)(
- u8 opcode, char *io_emul_stub, struct cpu_user_regs *regs);
-
static int debug_stack_lines = 20;
integer_param("debug_stack_lines", debug_stack_lines);
diff --git a/xen/include/asm-x86/io.h b/xen/include/asm-x86/io.h
index 8708b79b99..c4ec52cba7 100644
--- a/xen/include/asm-x86/io.h
+++ b/xen/include/asm-x86/io.h
@@ -49,8 +49,7 @@ __OUT(w,"w",short)
__OUT(l,,int)
/* Function pointer used to handle platform specific I/O port emulation. */
-#define IOEMUL_QUIRK_STUB_BYTES 10
-extern bool (*ioemul_handle_quirk)(
+extern unsigned int (*ioemul_handle_quirk)(
u8 opcode, char *io_emul_stub, struct cpu_user_regs *regs);
#endif
--
2.11.0
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