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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [Xen-changelog] [xen stable-4.6] x86: Support indirect thunks from assembly code
commit 9089da9cd06875be6c1022d59a6651cf3919da2e
Author: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
AuthorDate: Wed Feb 14 12:41:00 2018 +0100
Commit: Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Wed Feb 14 12:41:00 2018 +0100
x86: Support indirect thunks from assembly code
Introduce INDIRECT_CALL and INDIRECT_JMP which either degrade to a normal
indirect branch, or dispatch to the __x86_indirect_thunk_* symbols.
Update all the manual indirect branches in to use the new thunks. The
indirect branches in the early boot and kexec path are left intact as we
can't
use the compiled-in thunks at those points.
This is part of XSA-254.
Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
master commit: 7c508612f7a5096b4819d4ef2ce566e01bd66c0c
master date: 2018-01-16 17:45:50 +0000
---
xen/Rules.mk | 4 ++--
xen/arch/x86/Rules.mk | 6 +++++
xen/arch/x86/boot/trampoline.S | 24 +++++++++++++++++--
xen/arch/x86/traps.c | 41 ++++++++++++++++++++++----------
xen/arch/x86/x86_64/entry.S | 6 +++--
xen/arch/x86/x86_emulate/x86_emulate.c | 8 +++----
xen/common/wait.c | 8 ++++---
xen/include/asm-x86/asm_defns.h | 11 +++++++++
xen/include/asm-x86/indirect_thunk_asm.h | 41 ++++++++++++++++++++++++++++++++
9 files changed, 124 insertions(+), 25 deletions(-)
diff --git a/xen/Rules.mk b/xen/Rules.mk
index feb08d6..3c79b27 100644
--- a/xen/Rules.mk
+++ b/xen/Rules.mk
@@ -74,8 +74,8 @@ endif
AFLAGS-y += -D__ASSEMBLY__ -include
$(BASEDIR)/include/xen/config.h
-# Clang's built-in assembler can't handle .code16/.code32/.code64 yet
-AFLAGS-$(clang) += -no-integrated-as
+# Clang's built-in assembler can't handle embedded .include's
+CFLAGS-$(clang) += -no-integrated-as
ALL_OBJS := $(ALL_OBJS-y)
diff --git a/xen/arch/x86/Rules.mk b/xen/arch/x86/Rules.mk
index 4f79a5b..faf08ea 100644
--- a/xen/arch/x86/Rules.mk
+++ b/xen/arch/x86/Rules.mk
@@ -49,5 +49,11 @@ CFLAGS += -DCONFIG_INDIRECT_THUNK
export CONFIG_INDIRECT_THUNK=y
endif
+# Set up the assembler include path properly for older GCC toolchains. Clang
+# objects to the agument being passed however.
+ifneq ($(clang),y)
+CFLAGS += -Wa,-I$(BASEDIR)/include
+endif
+
CFLAGS-$(shadow-paging) += -DCONFIG_SHADOW_PAGING
CFLAGS-$(bigmem) += -DCONFIG_BIGMEM
diff --git a/xen/arch/x86/boot/trampoline.S b/xen/arch/x86/boot/trampoline.S
index ccb40fb..f46681c 100644
--- a/xen/arch/x86/boot/trampoline.S
+++ b/xen/arch/x86/boot/trampoline.S
@@ -109,8 +109,28 @@ trampoline_protmode_entry:
.code64
start64:
/* Jump to high mappings. */
- movabs $__high_start,%rax
- jmpq *%rax
+ movabs $__high_start, %rdi
+
+#ifdef CONFIG_INDIRECT_THUNK
+ /*
+ * If booting virtualised, or hot-onlining a CPU, sibling threads can
+ * attempt Branch Target Injection against this jmp.
+ *
+ * We've got no usable stack so can't use a RETPOLINE thunk, and are
+ * further than disp32 from the high mappings so couldn't use
+ * JUMP_THUNK even if it was a non-RETPOLINE thunk. Furthermore, an
+ * LFENCE isn't necessarily safe to use at this point.
+ *
+ * As this isn't a hotpath, use a fully serialising event to reduce
+ * the speculation window as much as possible. %ebx needs preserving
+ * for __high_start.
+ */
+ mov %ebx, %esi
+ cpuid
+ mov %esi, %ebx
+#endif
+
+ jmpq *%rdi
.code32
trampoline_boot_cpu_entry:
diff --git a/xen/arch/x86/traps.c b/xen/arch/x86/traps.c
index 16c6372..cd63a4d 100644
--- a/xen/arch/x86/traps.c
+++ b/xen/arch/x86/traps.c
@@ -1974,6 +1974,8 @@ static inline uint64_t guest_misc_enable(uint64_t val)
return val;
}
+void __x86_indirect_thunk_rcx(void);
+
/* Instruction fetch with error handling. */
#define insn_fetch(type, base, eip, limit) \
({ unsigned long _rc, _ptr = (base) + (eip); \
@@ -2022,6 +2024,8 @@ static int emulate_privileged_op(struct cpu_user_regs
*regs)
unsigned long code_base, code_limit;
char *io_emul_stub = NULL;
void (*io_emul)(struct cpu_user_regs *) __attribute__((__regparm__(1)));
+ struct stubs *this_stubs = &this_cpu(stubs);
+ unsigned long stub_va = this_stubs->addr + STUB_BUF_SIZE / 2;
uint64_t val;
bool_t vpmu_msr;
@@ -2210,31 +2214,44 @@ static int emulate_privileged_op(struct cpu_user_regs
*regs)
* context. This is needed for some systems which (ab)use IN/OUT
* to communicate with BIOS code in system-management mode.
*/
- io_emul_stub = map_domain_page(_mfn(this_cpu(stubs.mfn))) +
- (this_cpu(stubs.addr) & ~PAGE_MASK) +
- STUB_BUF_SIZE / 2;
+ io_emul_stub = map_domain_page(_mfn(this_stubs->mfn)) +
+ (stub_va & ~PAGE_MASK);
/* movq $host_to_guest_gpr_switch,%rcx */
io_emul_stub[0] = 0x48;
io_emul_stub[1] = 0xb9;
*(void **)&io_emul_stub[2] = (void *)host_to_guest_gpr_switch;
+
+#ifdef CONFIG_INDIRECT_THUNK
+ /* callq __x86_indirect_thunk_rcx */
+ io_emul_stub[10] = 0xe8;
+ *(int32_t *)&io_emul_stub[11] =
+ (long)__x86_indirect_thunk_rcx - (stub_va + 11 + 4);
+#else
/* callq *%rcx */
io_emul_stub[10] = 0xff;
io_emul_stub[11] = 0xd1;
+ /* TODO: untangle ideal_nops from init/livepatch Kconfig options. */
+ memcpy(&io_emul_stub[12], "\x0f\x1f\x00", 3); /* P6_NOP3 */
+#endif
+
/* data16 or nop */
- io_emul_stub[12] = (op_bytes != 2) ? 0x90 : 0x66;
+ io_emul_stub[15] = (op_bytes != 2) ? 0x90 : 0x66;
/* <io-access opcode> */
- io_emul_stub[13] = opcode;
+ io_emul_stub[16] = opcode;
/* imm8 or nop */
- io_emul_stub[14] = 0x90;
+ io_emul_stub[17] = 0x90;
/* ret (jumps to guest_to_host_gpr_switch) */
- io_emul_stub[15] = 0xc3;
- BUILD_BUG_ON(STUB_BUF_SIZE / 2 < 16);
+ io_emul_stub[18] = 0xc3;
+ BUILD_BUG_ON(STUB_BUF_SIZE / 2 < 19);
/* Handy function-typed pointer to the stub. */
- io_emul = (void *)(this_cpu(stubs.addr) + STUB_BUF_SIZE / 2);
+ io_emul = (void *)stub_va;
if ( ioemul_handle_quirk )
- ioemul_handle_quirk(opcode, &io_emul_stub[12], regs);
+ {
+ BUILD_BUG_ON(STUB_BUF_SIZE / 2 < 15 + 10);
+ ioemul_handle_quirk(opcode, &io_emul_stub[15], regs);
+ }
/* I/O Port and Interrupt Flag instructions. */
switch ( opcode )
@@ -2243,7 +2260,7 @@ static int emulate_privileged_op(struct cpu_user_regs
*regs)
op_bytes = 1;
case 0xe5: /* IN imm8,%eax */
port = insn_fetch(u8, code_base, eip, code_limit);
- io_emul_stub[14] = port; /* imm8 */
+ io_emul_stub[17] = port; /* imm8 */
exec_in:
if ( !guest_io_okay(port, op_bytes, v, regs) )
goto fail;
@@ -2272,7 +2289,7 @@ static int emulate_privileged_op(struct cpu_user_regs
*regs)
op_bytes = 1;
case 0xe7: /* OUT %eax,imm8 */
port = insn_fetch(u8, code_base, eip, code_limit);
- io_emul_stub[14] = port; /* imm8 */
+ io_emul_stub[17] = port; /* imm8 */
exec_out:
if ( !guest_io_okay(port, op_bytes, v, regs) )
goto fail;
diff --git a/xen/arch/x86/x86_64/entry.S b/xen/arch/x86/x86_64/entry.S
index b5188e4..008e22d 100644
--- a/xen/arch/x86/x86_64/entry.S
+++ b/xen/arch/x86/x86_64/entry.S
@@ -677,7 +677,8 @@ handle_exception_saved:
movzbl UREGS_entry_vector(%rsp),%eax
leaq exception_table(%rip),%rdx
PERFC_INCR(exceptions, %rax, %rbx)
- callq *(%rdx,%rax,8)
+ mov (%rdx, %rax, 8), %rdx
+ INDIRECT_CALL %rdx
mov %r15, STACK_CPUINFO_FIELD(xen_cr3)(%r14)
testb $3,UREGS_cs(%rsp)
jz restore_all_xen
@@ -848,7 +849,8 @@ handle_ist_exception:
1: movq %rsp,%rdi
movzbl UREGS_entry_vector(%rsp),%eax
leaq exception_table(%rip),%rdx
- callq *(%rdx,%rax,8)
+ mov (%rdx, %rax, 8), %rdx
+ INDIRECT_CALL %rdx
mov %r15, STACK_CPUINFO_FIELD(xen_cr3)(%r14)
cmpb $TRAP_nmi,UREGS_entry_vector(%rsp)
jne ret_from_intr
diff --git a/xen/arch/x86/x86_emulate/x86_emulate.c
b/xen/arch/x86/x86_emulate/x86_emulate.c
index 63fb761..f395534 100644
--- a/xen/arch/x86/x86_emulate/x86_emulate.c
+++ b/xen/arch/x86/x86_emulate/x86_emulate.c
@@ -4263,8 +4263,8 @@ x86_emulate(
if ( !rc )
{
copy_REX_VEX(buf, rex_prefix, vex);
- asm volatile ( "call *%0" : : "r" (stub.func), "a" (mmvalp)
- : "memory" );
+ asm volatile ( "INDIRECT_CALL %0" : : "r" (stub.func), "a" (mmvalp)
+ : "memory" );
}
put_fpu(&fic);
put_stub(stub);
@@ -4518,8 +4518,8 @@ x86_emulate(
if ( !rc )
{
copy_REX_VEX(buf, rex_prefix, vex);
- asm volatile ( "call *%0" : : "r" (stub.func), "a" (mmvalp)
- : "memory" );
+ asm volatile ( "INDIRECT_CALL %0" : : "r" (stub.func), "a" (mmvalp)
+ : "memory" );
}
put_fpu(&fic);
put_stub(stub);
diff --git a/xen/common/wait.c b/xen/common/wait.c
index 877ef19..6bb65c6 100644
--- a/xen/common/wait.c
+++ b/xen/common/wait.c
@@ -204,12 +204,14 @@ void check_wakeup_from_wait(void)
/*
* Hand-rolled longjmp(). Returns to the pointer on the top of
- * wqv->stack, and lands on a `rep movs` instruction.
+ * wqv->stack, and lands on a `rep movs` instruction. All other GPRs are
+ * restored from the stack, so are available for use here.
*/
asm volatile (
- "mov %1,%%"__OP"sp; jmp *(%0)"
+ "mov %1,%%"__OP"sp; INDIRECT_JMP %[ip]"
: : "S" (wqv->stack), "D" (wqv->esp),
- "c" ((char *)get_cpu_info() - (char *)wqv->esp)
+ "c" ((char *)get_cpu_info() - (char *)wqv->esp),
+ [ip] "r" (*(unsigned long *)wqv->stack)
: "memory" );
unreachable();
}
diff --git a/xen/include/asm-x86/asm_defns.h b/xen/include/asm-x86/asm_defns.h
index 0bb0589..1d6920c 100644
--- a/xen/include/asm-x86/asm_defns.h
+++ b/xen/include/asm-x86/asm_defns.h
@@ -13,6 +13,17 @@
#include <asm/cpufeature.h>
#include <asm/alternative.h>
+#ifdef __ASSEMBLY__
+# include <asm/indirect_thunk_asm.h>
+#else
+# ifdef CONFIG_INDIRECT_THUNK
+asm ( "\t.equ CONFIG_INDIRECT_THUNK, 1" );
+# else
+asm ( "\t.equ CONFIG_INDIRECT_THUNK, 0" );
+# endif
+asm ( "\t.include \"asm/indirect_thunk_asm.h\"" );
+#endif
+
#ifndef __ASSEMBLY__
void ret_from_intr(void);
#endif
diff --git a/xen/include/asm-x86/indirect_thunk_asm.h
b/xen/include/asm-x86/indirect_thunk_asm.h
new file mode 100644
index 0000000..96bcc25
--- /dev/null
+++ b/xen/include/asm-x86/indirect_thunk_asm.h
@@ -0,0 +1,41 @@
+/*
+ * Warning! This file is included at an assembler level for .c files, causing
+ * usual #ifdef'ary to turn into comments.
+ */
+
+.macro INDIRECT_BRANCH insn:req arg:req
+/*
+ * Create an indirect branch. insn is one of call/jmp, arg is a single
+ * register.
+ *
+ * With no compiler support, this degrades into a plain indirect call/jmp.
+ * With compiler support, dispatch to the correct __x86_indirect_thunk_*
+ */
+ .if CONFIG_INDIRECT_THUNK == 1
+
+ $done = 0
+ .irp reg, ax, cx, dx, bx, bp, si, di, 8, 9, 10, 11, 12, 13, 14, 15
+ .ifeqs "\arg", "%r\reg"
+ \insn __x86_indirect_thunk_r\reg
+ $done = 1
+ .exitm
+ .endif
+ .endr
+
+ .if $done != 1
+ .error "Bad register arg \arg"
+ .endif
+
+ .else
+ \insn *\arg
+ .endif
+.endm
+
+/* Convenience wrappers. */
+.macro INDIRECT_CALL arg:req
+ INDIRECT_BRANCH call \arg
+.endm
+
+.macro INDIRECT_JMP arg:req
+ INDIRECT_BRANCH jmp \arg
+.endm
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.6
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