[xen stable-4.10] x86: Support indirect thunks from assembly code

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[xen stable-4.10] x86: Support indirect thunks from assembly code

patchbot
commit 32babfc19ad3a3123f8ed4466df3c79492a2212b
Author:     Andrew Cooper <[hidden email]>
AuthorDate: Thu Feb 8 11:04:53 2018 +0100
Commit:     Jan Beulich <[hidden email]>
CommitDate: Thu Feb 8 11:04:53 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 <[hidden email]>
    Reviewed-by: Jan Beulich <[hidden email]>
    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/extable.c                   |  4 ++--
 xen/arch/x86/pv/emul-priv-op.c           | 39 +++++++++++++++++++++---------
 xen/arch/x86/x86_64/entry.S              |  6 +++--
 xen/arch/x86/x86_emulate/x86_emulate.c   |  4 ++--
 xen/common/wait.c                        |  8 ++++---
 xen/include/asm-x86/asm_defns.h          |  8 +++++++
 xen/include/asm-x86/indirect_thunk_asm.h | 41 ++++++++++++++++++++++++++++++++
 10 files changed, 120 insertions(+), 24 deletions(-)

diff --git a/xen/Rules.mk b/xen/Rules.mk
index 2659f8a..3cf4075 100644
--- a/xen/Rules.mk
+++ b/xen/Rules.mk
@@ -66,8 +66,8 @@ endif
 
 AFLAGS-y                += -D__ASSEMBLY__
 
-# 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 abcc4d4..70e9d8f 100644
--- a/xen/arch/x86/Rules.mk
+++ b/xen/arch/x86/Rules.mk
@@ -37,3 +37,9 @@ CFLAGS += -mindirect-branch=thunk-extern -mindirect-branch-register
 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
diff --git a/xen/arch/x86/boot/trampoline.S b/xen/arch/x86/boot/trampoline.S
index 4d640f3..f70d913 100644
--- a/xen/arch/x86/boot/trampoline.S
+++ b/xen/arch/x86/boot/trampoline.S
@@ -153,8 +153,28 @@ 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
 
 #include "wakeup.S"
 
diff --git a/xen/arch/x86/extable.c b/xen/arch/x86/extable.c
index 6fffe05..72f30d9 100644
--- a/xen/arch/x86/extable.c
+++ b/xen/arch/x86/extable.c
@@ -158,7 +158,7 @@ static int __init stub_selftest(void)
         memcpy(ptr, tests[i].opc, ARRAY_SIZE(tests[i].opc));
         unmap_domain_page(ptr);
 
-        asm volatile ( "call *%[stb]\n"
+        asm volatile ( "INDIRECT_CALL %[stb]\n"
                        ".Lret%=:\n\t"
                        ".pushsection .fixup,\"ax\"\n"
                        ".Lfix%=:\n\t"
@@ -167,7 +167,7 @@ static int __init stub_selftest(void)
                        ".popsection\n\t"
                        _ASM_EXTABLE(.Lret%=, .Lfix%=)
                        : [exn] "+m" (res)
-                       : [stb] "rm" (addr), "a" (tests[i].rax));
+                       : [stb] "r" (addr), "a" (tests[i].rax));
         ASSERT(res == tests[i].res.raw);
     }
 
diff --git a/xen/arch/x86/pv/emul-priv-op.c b/xen/arch/x86/pv/emul-priv-op.c
index 5f23c2c..b965b3e 100644
--- a/xen/arch/x86/pv/emul-priv-op.c
+++ b/xen/arch/x86/pv/emul-priv-op.c
@@ -73,37 +73,54 @@ void (*pv_post_outb_hook)(unsigned int port, u8 value);
 
 typedef void io_emul_stub_t(struct cpu_user_regs *);
 
+void __x86_indirect_thunk_rcx(void);
+
 static io_emul_stub_t *io_emul_stub_setup(struct priv_op_ctxt *ctxt, u8 opcode,
                                           unsigned int port, unsigned int bytes)
 {
+    struct stubs *this_stubs = &this_cpu(stubs);
+    unsigned long stub_va = this_stubs->addr + STUB_BUF_SIZE / 2;
+
     if ( !ctxt->io_emul_stub )
-        ctxt->io_emul_stub = map_domain_page(_mfn(this_cpu(stubs.mfn))) +
-                                             (this_cpu(stubs.addr) &
-                                              ~PAGE_MASK) +
-                                             STUB_BUF_SIZE / 2;
+        ctxt->io_emul_stub =
+            map_domain_page(_mfn(this_stubs->mfn)) + (stub_va & ~PAGE_MASK);
 
     /* movq $host_to_guest_gpr_switch,%rcx */
     ctxt->io_emul_stub[0] = 0x48;
     ctxt->io_emul_stub[1] = 0xb9;
     *(void **)&ctxt->io_emul_stub[2] = (void *)host_to_guest_gpr_switch;
+
+#ifdef CONFIG_INDIRECT_THUNK
+    /* callq __x86_indirect_thunk_rcx */
+    ctxt->io_emul_stub[10] = 0xe8;
+    *(int32_t *)&ctxt->io_emul_stub[11] =
+        (long)__x86_indirect_thunk_rcx - (stub_va + 11 + 4);
+#else
     /* callq *%rcx */
     ctxt->io_emul_stub[10] = 0xff;
     ctxt->io_emul_stub[11] = 0xd1;
+    /* TODO: untangle ideal_nops from init/livepatch Kconfig options. */
+    memcpy(&ctxt->io_emul_stub[12], "\x0f\x1f\x00", 3); /* P6_NOP3 */
+#endif
+
     /* data16 or nop */
-    ctxt->io_emul_stub[12] = (bytes != 2) ? 0x90 : 0x66;
+    ctxt->io_emul_stub[15] = (bytes != 2) ? 0x90 : 0x66;
     /* <io-access opcode> */
-    ctxt->io_emul_stub[13] = opcode;
+    ctxt->io_emul_stub[16] = opcode;
     /* imm8 or nop */
-    ctxt->io_emul_stub[14] = !(opcode & 8) ? port : 0x90;
+    ctxt->io_emul_stub[17] = !(opcode & 8) ? port : 0x90;
     /* ret (jumps to guest_to_host_gpr_switch) */
-    ctxt->io_emul_stub[15] = 0xc3;
-    BUILD_BUG_ON(STUB_BUF_SIZE / 2 < 16);
+    ctxt->io_emul_stub[18] = 0xc3;
+    BUILD_BUG_ON(STUB_BUF_SIZE / 2 < 19);
 
     if ( ioemul_handle_quirk )
-        ioemul_handle_quirk(opcode, &ctxt->io_emul_stub[12], ctxt->ctxt.regs);
+    {
+        BUILD_BUG_ON(STUB_BUF_SIZE / 2 < 15 + 10);
+        ioemul_handle_quirk(opcode, &ctxt->io_emul_stub[15], ctxt->ctxt.regs);
+    }
 
     /* Handy function-typed pointer to the stub. */
-    return (void *)(this_cpu(stubs.addr) + STUB_BUF_SIZE / 2);
+    return (void *)stub_va;
 }
 
 
diff --git a/xen/arch/x86/x86_64/entry.S b/xen/arch/x86/x86_64/entry.S
index a8825c8..710c061 100644
--- a/xen/arch/x86/x86_64/entry.S
+++ b/xen/arch/x86/x86_64/entry.S
@@ -585,7 +585,8 @@ 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
@@ -757,7 +758,8 @@ 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 820495f..ff0a003 100644
--- a/xen/arch/x86/x86_emulate/x86_emulate.c
+++ b/xen/arch/x86/x86_emulate/x86_emulate.c
@@ -867,7 +867,7 @@ static inline int mkec(uint8_t e, int32_t ec, ...)
 #ifdef __XEN__
 # define invoke_stub(pre, post, constraints...) do {                    \
     union stub_exception_token res_ = { .raw = ~0 };                    \
-    asm volatile ( pre "\n\tcall *%[stub]\n\t" post "\n"                \
+    asm volatile ( pre "\n\tINDIRECT_CALL %[stub]\n\t" post "\n"        \
                    ".Lret%=:\n\t"                                       \
                    ".pushsection .fixup,\"ax\"\n"                       \
                    ".Lfix%=:\n\t"                                       \
@@ -876,7 +876,7 @@ static inline int mkec(uint8_t e, int32_t ec, ...)
                    ".popsection\n\t"                                    \
                    _ASM_EXTABLE(.Lret%=, .Lfix%=)                       \
                    : [exn] "+g" (res_), constraints,                    \
-                     [stub] "rm" (stub.func),                           \
+                     [stub] "r" (stub.func),                            \
                      "m" (*(uint8_t(*)[MAX_INST_LEN + 1])stub.ptr) );   \
     if ( unlikely(~res_.raw) )                                          \
     {                                                                   \
diff --git a/xen/common/wait.c b/xen/common/wait.c
index 3d3d9fe..a57bc10 100644
--- a/xen/common/wait.c
+++ b/xen/common/wait.c
@@ -203,12 +203,14 @@ 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 73d9622..9cfd79f 100644
--- a/xen/include/asm-x86/asm_defns.h
+++ b/xen/include/asm-x86/asm_defns.h
@@ -13,6 +13,14 @@
 #include <asm/cpufeature.h>
 #include <asm/alternative.h>
 
+#ifdef __ASSEMBLY__
+# include <asm/indirect_thunk_asm.h>
+#else
+asm ( "\t.equ CONFIG_INDIRECT_THUNK, "
+      __stringify(IS_ENABLED(CONFIG_INDIRECT_THUNK)) );
+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-4.10

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