livepatch: Initial ARM32 support.

The patch piggybacks on: livepatch: Initial ARM64 support, which
brings up all of the necessary livepatch infrastructure pieces in.

This patch adds three major pieces:

 1) ELF relocations. ARM32 uses SHT_REL instead of SHT_RELA which
    means the adddendum had to be extracted from within the
    instruction. Which required parsing BL/BLX, B/BL<cond>,
    MOVT, and MOVW instructions.

    The code was written from scratch using the ARM ELF manual
    (and the ARM Architecture Reference Manual)

 2) Inserting an trampoline. We use the B (branch to address)
    which uses an offset that is based on the PC value: PC + imm32.
    Because we insert the branch at the start of the old function
    we have to account for the instruction already being fetched
    and subtract -8 from the delta (new_addr - old_addr). See
    ARM DDI 0406C.c, see A2.3 (pg 45) and A8.8.18 pg (pg 334,335)

 3) Allows the test-cases to be built under ARM 32.
    The "livepatch: tests: Make them compile under ARM64"
    put in the right infrastructure for it and we piggyback on it.

Acked-by: Julien Grall <julien.grall@arm.com>
Acked-by: Jan Beulich <jbeulich@suse.com> [for non-ARM parts]
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

xen/arch/arm/arm32/livepatch.c

@@ -3,21 +3,111 @@
  */
 
 #include <xen/errno.h>
+#include <xen/kernel.h>
 #include <xen/lib.h>
 #include <xen/livepatch_elf.h>
 #include <xen/livepatch.h>
 
+#include <asm/page.h>
+#include <asm/livepatch.h>
+
 void arch_livepatch_apply(struct livepatch_func *func)
 {
+    uint32_t insn;
+    uint32_t *new_ptr;
+    unsigned int i, len;
+
+    BUILD_BUG_ON(ARCH_PATCH_INSN_SIZE > sizeof(func->opaque));
+    BUILD_BUG_ON(ARCH_PATCH_INSN_SIZE != sizeof(insn));
+
+    ASSERT(vmap_of_xen_text);
+
+    len = livepatch_insn_len(func);
+    if ( !len )
+        return;
+
+    /* Save old ones. */
+    memcpy(func->opaque, func->old_addr, len);
+
+    if ( func->new_addr )
+    {
+        s32 delta;
+
+        /*
+         * PC is current address (old_addr) + 8 bytes. The semantics for a
+         * unconditional branch is to jump to PC + imm32 (offset).
+         *
+         * ARM DDI 0406C.c, see A2.3 (pg 45) and A8.8.18 pg (pg 334,335)
+         *
+         */
+        delta = (s32)func->new_addr - (s32)(func->old_addr + 8);
+
+        /* The arch_livepatch_symbol_ok should have caught it. */
+        ASSERT(delta >= -(s32)ARCH_LIVEPATCH_RANGE ||
+               delta < (s32)ARCH_LIVEPATCH_RANGE);
+
+        /* CPU shifts by two (left) when decoding, so we shift right by two. */
+        delta = delta >> 2;
+        /* Lets not modify the cond. */
+        delta &= 0x00FFFFFF;
+
+        insn = 0xea000000 | delta;
+    }
+    else
+        insn = 0xe1a00000; /* mov r0, r0 */
+
+    new_ptr = func->old_addr - (void *)_start + vmap_of_xen_text;
+    len = len / sizeof(uint32_t);
+
+    /* PATCH! */
+    for ( i = 0; i < len; i++ )
+        *(new_ptr + i) = insn;
+
+    /*
+    * When we upload the payload, it will go through the data cache
+    * (the region is cacheable). Until the data cache is cleaned, the data
+    * may not reach the memory. And in the case the data and instruction cache
+    * are separated, we may read invalid instruction from the memory because
+    * the data cache have not yet synced with the memory. Hence sync it.
+    */
+    if ( func->new_addr )
+        clean_and_invalidate_dcache_va_range(func->new_addr, func->new_size);
+    clean_and_invalidate_dcache_va_range(new_ptr, sizeof (*new_ptr) * len);
 }
 
 void arch_livepatch_revert(const struct livepatch_func *func)
 {
+    uint32_t *new_ptr;
+    unsigned int len;
+
+    new_ptr = func->old_addr - (void *)_start + vmap_of_xen_text;
+
+    len = livepatch_insn_len(func);
+    memcpy(new_ptr, func->opaque, len);
+
+    clean_and_invalidate_dcache_va_range(new_ptr, len);
 }
 
 int arch_livepatch_verify_elf(const struct livepatch_elf *elf)
 {
-    return -EOPNOTSUPP;
+    const Elf_Ehdr *hdr = elf->hdr;
+
+    if ( hdr->e_machine != EM_ARM ||
+         hdr->e_ident[EI_CLASS] != ELFCLASS32 )
+    {
+        dprintk(XENLOG_ERR, LIVEPATCH "%s: Unsupported ELF Machine type!\n",
+                elf->name);
+        return -EOPNOTSUPP;
+    }
+
+    if ( (hdr->e_flags & EF_ARM_EABI_MASK) != EF_ARM_EABI_VER5 )
+    {
+        dprintk(XENLOG_ERR, LIVEPATCH "%s: Unsupported ELF EABI(%x)!\n",
+                elf->name, hdr->e_flags);
+        return -EOPNOTSUPP;
+    }
+
+    return 0;
 }
 
 bool arch_livepatch_symbol_deny(const struct livepatch_elf *elf,
@@ -33,11 +123,193 @@ bool arch_livepatch_symbol_deny(const struct livepatch_elf *elf,
     return false;
 }
 
+static s32 get_addend(unsigned char type, void *dest)
+{
+    s32 addend = 0;
+
+    switch ( type ) {
+    case R_ARM_NONE:
+        /* ignore */
+        break;
+
+    case R_ARM_ABS32:
+        addend = *(u32 *)dest;
+        break;
+
+    case R_ARM_REL32:
+        addend = *(u32 *)dest;
+        break;
+
+    case R_ARM_MOVW_ABS_NC:
+    case R_ARM_MOVT_ABS:
+        addend =  (*(u32 *)dest & 0x00000FFF);
+        addend |= (*(u32 *)dest & 0x000F0000) >> 4;
+        /* Addend is to sign-extend ([19:16],[11:0]). */
+        addend = (s16)addend;
+        break;
+
+    case R_ARM_CALL:
+    case R_ARM_JUMP24:
+        /* Addend = sign_extend (insn[23:0]) << 2 */
+        addend = ((*(u32 *)dest & 0xFFFFFF) ^ 0x800000) - 0x800000;
+        addend = addend << 2;
+        break;
+    }
+
+    return addend;
+}
+
+static int perform_rel(unsigned char type, void *dest, uint32_t val, s32 addend)
+{
+
+    switch ( type ) {
+    case R_ARM_NONE:
+        /* ignore */
+        break;
+
+    case R_ARM_ABS32: /* (S + A) | T */
+        *(u32 *)dest = (val + addend);
+        break;
+
+    case R_ARM_REL32: /* ((S + A) | T) – P */
+        *(u32 *)dest = (val + addend) - (uint32_t)dest;
+        break;
+
+    case R_ARM_MOVW_ABS_NC: /* S + A */
+    case R_ARM_MOVT_ABS: /* S + A */
+        /* Clear addend if needed . */
+        if ( addend )
+            *(u32 *)dest &= 0xFFF0F000;
+
+        if ( type == R_ARM_MOVT_ABS )
+        {
+            /*
+             * Almost the same as MOVW except it uses the 16 bit
+             * high value. Putting it in insn requires shifting right by
+             * 16-bit (as we only have 16-bit for imm.
+             */
+            val &= 0xFFFF0000; /* ResultMask */
+            val = val >> 16;
+        }
+        else
+        {
+            /* MOVW loads 16 bits into the bottom half of a register. */
+            val &= 0xFFFF;
+        }
+        /* [11:0] = Result_Mask(X) & 0xFFF,[19:16] = Result_Mask(X) >> 12 */
+        *(u32 *)dest |= val & 0xFFF;
+        *(u32 *)dest |= (val >> 12) << 16;
+        break;
+
+    case R_ARM_CALL:
+    case R_ARM_JUMP24: /* (S + A) - P */
+        /* Clear the old addend. */
+        if ( addend )
+            *(u32 *)dest &= 0xFF000000;
+
+        val += addend - (uint32_t)dest;
+
+        /*
+         * arch_livepatch_verify_distance can't account of addend so we have
+         * to do the check here as well.
+         */
+        if ( (s32)val < -(s32)ARCH_LIVEPATCH_RANGE ||
+             (s32)val >= (s32)ARCH_LIVEPATCH_RANGE )
+            return -EOVERFLOW;
+
+        /* CPU always shifts insn by two, so complement it. */
+        val = val >> 2;
+        val &= 0x00FFFFFE;
+        *(u32 *)dest |= (uint32_t)val;
+        break;
+
+    default:
+         return -EOPNOTSUPP;
+    }
+
+    return 0;
+}
+
+int arch_livepatch_perform(struct livepatch_elf *elf,
+                           const struct livepatch_elf_sec *base,
+                           const struct livepatch_elf_sec *rela,
+                           bool use_rela)
+{
+    const Elf_RelA *r_a;
+    const Elf_Rel *r;
+    unsigned int symndx, i;
+    uint32_t val;
+    void *dest;
+    int rc = 0;
+
+    for ( i = 0; i < (rela->sec->sh_size / rela->sec->sh_entsize); i++ )
+    {
+        unsigned char type;
+        s32 addend = 0;
+
+        if ( use_rela )
+        {
+            r_a = rela->data + i * rela->sec->sh_entsize;
+            symndx = ELF32_R_SYM(r_a->r_info);
+            type = ELF32_R_TYPE(r_a->r_info);
+            dest = base->load_addr + r_a->r_offset; /* P */
+            addend = r_a->r_addend;
+        }
+        else
+        {
+            r = rela->data + i * rela->sec->sh_entsize;
+            symndx = ELF32_R_SYM(r->r_info);
+            type = ELF32_R_TYPE(r->r_info);
+            dest = base->load_addr + r->r_offset; /* P */
+        }
+
+        if ( symndx > elf->nsym )
+        {
+            dprintk(XENLOG_ERR, LIVEPATCH "%s: Relative symbol wants symbol@%u which is past end!\n",
+                    elf->name, symndx);
+            return -EINVAL;
+        }
+
+        if ( !use_rela )
+            addend = get_addend(type, dest);
+
+        val = elf->sym[symndx].sym->st_value; /* S */
+
+        rc = perform_rel(type, dest, val, addend);
+        switch ( rc ) {
+        case -EOVERFLOW:
+            dprintk(XENLOG_ERR, LIVEPATCH "%s: Overflow in relocation %u in %s for %s!\n",
+                    elf->name, i, rela->name, base->name);
+            break;
+
+        case -EOPNOTSUPP:
+            dprintk(XENLOG_ERR, LIVEPATCH "%s: Unhandled relocation #%x\n",
+                    elf->name, type);
+            break;
+
+        default:
+            break;
+        }
+
+        if ( rc )
+            break;
+    }
+
+    return rc;
+}
+
+int arch_livepatch_perform_rel(struct livepatch_elf *elf,
+                               const struct livepatch_elf_sec *base,
+                               const struct livepatch_elf_sec *rela)
+{
+    return arch_livepatch_perform(elf, base, rela, false);
+}
+
 int arch_livepatch_perform_rela(struct livepatch_elf *elf,
                                 const struct livepatch_elf_sec *base,
                                 const struct livepatch_elf_sec *rela)
 {
-    return -ENOSYS;
+    return arch_livepatch_perform(elf, base, rela, true);
 }
 
 /*

xen/arch/arm/arm64/livepatch.c

@@ -241,6 +241,13 @@ static int reloc_insn_imm(enum aarch64_reloc_op op, void *dest, u64 val,
     return 0;
 }
 
+int arch_livepatch_perform_rel(struct livepatch_elf *elf,
+                               const struct livepatch_elf_sec *base,
+                               const struct livepatch_elf_sec *rela)
+{
+    return -ENOSYS;
+}
+
 int arch_livepatch_perform_rela(struct livepatch_elf *elf,
                                 const struct livepatch_elf_sec *base,
                                 const struct livepatch_elf_sec *rela)

xen/arch/arm/livepatch.c

@@ -118,13 +118,6 @@ bool arch_livepatch_symbol_ok(const struct livepatch_elf *elf,
     return true;
 }
 
-int arch_livepatch_perform_rel(struct livepatch_elf *elf,
-                               const struct livepatch_elf_sec *base,
-                               const struct livepatch_elf_sec *rela)
-{
-    return -ENOSYS;
-}
-
 int arch_livepatch_secure(const void *va, unsigned int pages, enum va_type type)
 {
     unsigned long start = (unsigned long)va;

xen/common/Kconfig

@@ -217,7 +217,7 @@ config CRYPTO
 config LIVEPATCH
 	bool "Live patching support (TECH PREVIEW)"
 	default n
-	depends on !ARM_32 && HAS_BUILD_ID = "y"
+	depends on HAS_BUILD_ID = "y"
 	---help---
 	  Allows a running Xen hypervisor to be dynamically patched using
 	  binary patches without rebooting. This is primarily used to binarily

xen/include/xen/elfstructs.h

@@ -103,6 +103,15 @@ typedef uint64_t	Elf64_Xword;
                       (ehdr).e_ident[EI_MAG2] == ELFMAG2 && \
                       (ehdr).e_ident[EI_MAG3] == ELFMAG3)
 
+/* e_flags */
+#define EF_ARM_EABI_MASK	0xff000000
+#define EF_ARM_EABI_UNKNOWN	0x00000000
+#define EF_ARM_EABI_VER1	0x01000000
+#define EF_ARM_EABI_VER2	0x02000000
+#define EF_ARM_EABI_VER3	0x03000000
+#define EF_ARM_EABI_VER4	0x04000000
+#define EF_ARM_EABI_VER5	0x05000000
+
 /* ELF Header */
 typedef struct elfhdr {
 	unsigned char	e_ident[EI_NIDENT]; /* ELF Identification */
@@ -364,9 +373,22 @@ typedef struct {
 #define R_X86_64_PLT32		4	/* 32 bit PLT address */
 
 /*
+ * ARM32 relocation types. See
+ * http://infocenter.arm.com/help/topic/com.arm.doc.ihi0044f/IHI0044F_aaelf.pdf
  * S - address of symbol.
- * A - addend for relocation (r_addend)
+ * A - addend for relocation (r_addend or need to extract from insn)
  * P - address of the dest being relocated (derieved from r_offset)
+ */
+#define R_ARM_NONE              0
+#define R_ARM_ABS32             2	/* Direct 32-bit. S+A */
+#define R_ARM_REL32             3	/* PC relative. S+A */
+#define R_ARM_CALL              28	/* SignExtend([23:0]) << 2. S+A-P */
+#define R_ARM_JUMP24            29	/* Same as R_ARM_CALL */
+#define R_ARM_MOVW_ABS_NC       43	/* SignExtend([19:16],[11:0])&0xFFFF, S+A */
+#define R_ARM_MOVT_ABS          44	/* SignExtend([19:16],[11:0))&0xFFFF0000 */
+					/*  >> 16, S+A. */
+
+/*
  * NC -  No check for overflow.
  *
  * The defines also use _PREL for PC-relative address, and _NC is No Check.

xen/test/Makefile

@@ -1,8 +1,6 @@
 .PHONY: tests
 tests:
-ifneq $(XEN_TARGET_ARCH),arm32)
 	$(MAKE) -f $(BASEDIR)/Rules.mk -C livepatch livepatch
-endif
 
 .PHONY: clean
 clean::

xen/test/livepatch/Makefile

@@ -6,6 +6,9 @@ endif
 ifeq ($(XEN_TARGET_ARCH),arm64)
 OBJCOPY_MAGIC := -I binary -O elf64-littleaarch64 -B aarch64
 endif
+ifeq ($(XEN_TARGET_ARCH),arm32)
+OBJCOPY_MAGIC := -I binary -O elf32-littlearm -B arm
+endif
 
 CODE_ADDR=$(shell nm --defined $(1) | grep $(2) | awk '{print "0x"$$1}')
 CODE_SZ=$(shell nm --defined -S $(1) | grep $(2) | awk '{ print "0x"$$2}')