[Xen-devel] [PATCH v3 05/23] xsplice: Add helper elf routines (v4)

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

From: Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>

Add Elf routines and data structures in preparation for loading an
xSplice payload.

We also add an macro that will print where we failed during
the ELF parsing - which is only available during debug builds.
In production (debug=n) we only return the error value.

Signed-off-by: Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
---
v2: - With the #define ELFSIZE in the ARM file we can use the common
     #defines instead of using #ifdef CONFIG_ARM_32. Moved to another
    patch.
    - Add checks for ELF file.
    - Add name to be printed.
    - Add len for easier ELF checks.
    - Expand on the checks. Add macro.
v3: Remove the return_ macro
v4: Add return_ macro back but make it depend on debug=y
---
 xen/common/Makefile           |   1 +
 xen/common/xsplice_elf.c      | 205 ++++++++++++++++++++++++++++++++++++++++++
 xen/include/xen/xsplice_elf.h |  37 ++++++++
 3 files changed, 243 insertions(+)
 create mode 100644 xen/common/xsplice_elf.c
 create mode 100644 xen/include/xen/xsplice_elf.h

diff --git a/xen/common/Makefile b/xen/common/Makefile
index 43b3911..a8ceaff 100644
--- a/xen/common/Makefile
+++ b/xen/common/Makefile
@@ -74,3 +74,4 @@ subdir-y += libelf
 subdir-$(CONFIG_HAS_DEVICE_TREE) += libfdt
 
 obj-$(CONFIG_XSPLICE) += xsplice.o
+obj-$(CONFIG_XSPLICE) += xsplice_elf.o
diff --git a/xen/common/xsplice_elf.c b/xen/common/xsplice_elf.c
new file mode 100644
index 0000000..d9f9002
--- /dev/null
+++ b/xen/common/xsplice_elf.c
@@ -0,0 +1,205 @@
+#include <xen/errno.h>
+#include <xen/lib.h>
+#include <xen/xsplice_elf.h>
+#include <xen/xsplice.h>
+
+#ifdef NDEBUG
+#define return_(x) return x
+#else
+#define return_(x) { printk(XENLOG_DEBUG "%s:%d rc: %d\n",  \
+                            __func__,__LINE__, x); return x; }
+#endif
+
+struct xsplice_elf_sec *xsplice_elf_sec_by_name(const struct xsplice_elf *elf,
+                                                const char *name)
+{
+    unsigned int i;
+
+    for ( i = 0; i < elf->hdr->e_shnum; i++ )
+    {
+        if ( !strcmp(name, elf->sec[i].name) )
+            return &elf->sec[i];
+    }
+
+    return NULL;
+}
+
+static int elf_resolve_sections(struct xsplice_elf *elf, uint8_t *data)
+{
+    struct xsplice_elf_sec *sec;
+    unsigned int i;
+
+    sec = xmalloc_array(struct xsplice_elf_sec, elf->hdr->e_shnum);
+    if ( !sec )
+    {
+        printk(XENLOG_ERR "Could not allocate memory for section table!\n");
+        return_(-ENOMEM);
+    }
+
+    /* N.B. We also will ingest SHN_UNDEF sections. */
+    for ( i = 0; i < elf->hdr->e_shnum; i++ )
+    {
+        ssize_t delta = elf->hdr->e_shoff + i * elf->hdr->e_shentsize;
+
+        if ( delta + sizeof(Elf_Shdr) > elf->len )
+            return_(-EINVAL);
+
+        sec[i].sec = (Elf_Shdr *)(data + delta);
+        delta = sec[i].sec->sh_offset;
+
+        if ( delta > elf->len )
+            return_(-EINVAL);
+
+        sec[i].data = data + delta;
+        /* Name is populated in xsplice_elf_sections_name. */
+        sec[i].name = NULL;
+
+        if ( sec[i].sec->sh_type == SHT_SYMTAB )
+        {
+                if ( elf->symtab )
+                    return_(-EINVAL);
+                elf->symtab = &sec[i];
+                /* elf->symtab->sec->sh_link would point to the right section
+                 * but we hadn't finished parsing all the sections. */
+                if ( elf->symtab->sec->sh_link > elf->hdr->e_shnum )
+                    return_(-EINVAL);
+        }
+    }
+    elf->sec = sec;
+    if ( !elf->symtab )
+        return_(-EINVAL);
+
+    /* There can be multiple SHT_STRTAB so pick the right one. */
+    elf->strtab = &sec[elf->symtab->sec->sh_link];
+
+    if ( elf->symtab->sec->sh_size == 0 || elf->symtab->sec->sh_entsize == 0 )
+        return_(-EINVAL);
+
+    if ( elf->symtab->sec->sh_entsize != sizeof(Elf_Sym) )
+        return_(-EINVAL);
+
+    return 0;
+}
+
+static int elf_resolve_section_names(struct xsplice_elf *elf, uint8_t *data)
+{
+    const char *shstrtab;
+    unsigned int i;
+    unsigned int offset, delta;
+
+    /* The elf->sec[0 -> e_shnum] structures have been verified by 
elf_resolve_sections */
+    /* Find file offset for section string table. */
+    offset =  elf->sec[elf->hdr->e_shstrndx].sec->sh_offset;
+
+    if ( offset > elf->len )
+        return_(-EINVAL);
+
+    shstrtab = (const char *)(data + offset);
+
+    /* We could ignore the first as it is reserved.. */
+    for ( i = 0; i < elf->hdr->e_shnum; i++ )
+    {
+        delta = elf->sec[i].sec->sh_name;
+
+        if ( offset + delta > elf->len )
+            return_(-EINVAL);
+
+        elf->sec[i].name = shstrtab + delta;
+    }
+    return 0;
+}
+
+static int elf_get_sym(struct xsplice_elf *elf, uint8_t *data)
+{
+    struct xsplice_elf_sec *symtab_sec, *strtab_sec;
+    struct xsplice_elf_sym *sym;
+    unsigned int i, delta, offset;
+
+    symtab_sec = elf->symtab;
+
+    strtab_sec = elf->strtab;
+
+    /* Pointers arithmetic to get file offset. */
+    offset = strtab_sec->data - data;
+
+    ASSERT( offset == strtab_sec->sec->sh_offset );
+    /* symtab_sec->data was computed in elf_resolve_sections. */
+    ASSERT((symtab_sec->sec->sh_offset + data) == symtab_sec->data );
+
+    /* No need to check values as elf_resolve_sections did it. */
+    elf->nsym = symtab_sec->sec->sh_size / symtab_sec->sec->sh_entsize;
+
+    sym = xmalloc_array(struct xsplice_elf_sym, elf->nsym);
+    if ( !sym )
+    {
+        printk(XENLOG_ERR "%s: Could not allocate memory for symbols\n", 
elf->name);
+        return_(-ENOMEM);
+    }
+
+    for ( i = 0; i < elf->nsym; i++ )
+    {
+        Elf_Sym *s;
+
+        if ( i * sizeof(Elf_Sym) > elf->len )
+            return_(-EINVAL);
+
+        s = &((Elf_Sym *)symtab_sec->data)[i];
+
+        /* If st->name is STN_UNDEF it is zero, so the check will always be 
true. */
+        delta = s->st_name;
+        /* Offset has been computed earlier. */
+        if ( offset + delta > elf->len )
+            return_(-EINVAL);
+
+        sym[i].sym = s;
+        if ( s->st_name == STN_UNDEF )
+            sym[i].name = NULL;
+        else
+            sym[i].name = (const char *)data + ( delta + offset );
+    }
+    elf->sym = sym;
+
+    return 0;
+}
+
+int xsplice_elf_load(struct xsplice_elf *elf, uint8_t *data)
+{
+    int rc;
+
+    elf->hdr = (Elf_Ehdr *)data;
+
+    if ( sizeof(*elf->hdr) >= elf->len )
+        return_(-EINVAL);
+
+    if ( elf->hdr->e_shstrndx == SHN_UNDEF )
+        return_(-EINVAL);
+
+    /* Check that section name index is within the sections. */
+    if ( elf->hdr->e_shstrndx > elf->hdr->e_shnum )
+        return_(-EINVAL);
+
+    rc = elf_resolve_sections(elf, data);
+    if ( rc )
+        return rc;
+
+    rc = elf_resolve_section_names(elf, data);
+    if ( rc )
+        return rc;
+
+    rc = elf_get_sym(elf, data);
+    if ( rc )
+        return rc;
+
+    return 0;
+}
+
+void xsplice_elf_free(struct xsplice_elf *elf)
+{
+    xfree(elf->sec);
+    elf->sec = NULL;
+    xfree(elf->sym);
+    elf->sym = NULL;
+    elf->nsym = 0;
+    elf->name = NULL;
+    elf->len = 0;
+}
diff --git a/xen/include/xen/xsplice_elf.h b/xen/include/xen/xsplice_elf.h
new file mode 100644
index 0000000..42dbc6f
--- /dev/null
+++ b/xen/include/xen/xsplice_elf.h
@@ -0,0 +1,37 @@
+#ifndef __XEN_XSPLICE_ELF_H__
+#define __XEN_XSPLICE_ELF_H__
+
+#include <xen/types.h>
+#include <xen/elfstructs.h>
+
+/* The following describes an Elf file as consumed by xSplice. */
+struct xsplice_elf_sec {
+    Elf_Shdr *sec;                 /* Hooked up in elf_resolve_sections. */
+    const char *name;              /* Human readable name hooked in
+                                      elf_resolve_section_names. */
+    const uint8_t *data;           /* Pointer to the section (done by
+                                      elf_resolve_sections). */
+};
+
+struct xsplice_elf_sym {
+    Elf_Sym *sym;
+    const char *name;
+};
+
+struct xsplice_elf {
+    const char *name;              /* Pointer to payload->name. */
+    ssize_t len;                   /* Length of the ELF file. */
+    Elf_Ehdr *hdr;                 /* ELF file. */
+    struct xsplice_elf_sec *sec;   /* Array of sections, allocated by us. */
+    struct xsplice_elf_sym *sym;   /* Array of symbols , allocated by us. */
+    unsigned int nsym;
+    struct xsplice_elf_sec *symtab;/* Pointer to .symtab section - aka to 
sec[x]. */
+    struct xsplice_elf_sec *strtab;/* Pointer to .strtab section - aka to 
sec[y]. */
+};
+
+struct xsplice_elf_sec *xsplice_elf_sec_by_name(const struct xsplice_elf *elf,
+                                                const char *name);
+int xsplice_elf_load(struct xsplice_elf *elf, uint8_t *data);
+void xsplice_elf_free(struct xsplice_elf *elf);
+
+#endif /* __XEN_XSPLICE_ELF_H__ */
-- 
2.1.0


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