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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [Xen-devel] [PATCH 2/5] libelf: rewrite symtab/strtab loading for Dom0
Current implementation of elf_load_bsdsyms is broken when loading inside of
a HVM guest, because it assumes elf_memcpy_safe is able to write into guest
memory space, which it is not.
Take the oportunity to do some cleanup and properly document how
elf_{parse/load}_bsdsyms works. The new implementation uses elf_load_image
when dealing with data that needs to be copied to the guest memory space.
Also reduce the number of section headers copied to the minimum necessary.
Signed-off-by: Roger Pau Monnà <roger.pau@xxxxxxxxxx>
---
Cc: Ian Campbell <ian.campbell@xxxxxxxxxx>
Cc: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
Cc: Jan Beulich <jbeulich@xxxxxxxx>
Cc: Keir Fraser <keir@xxxxxxx>
Cc: Tim Deegan <tim@xxxxxxx>
---
xen/common/libelf/libelf-loader.c | 213 ++++++++++++++++++++++++++++----------
1 file changed, 158 insertions(+), 55 deletions(-)
diff --git a/xen/common/libelf/libelf-loader.c
b/xen/common/libelf/libelf-loader.c
index 6f42bea..9552d4c 100644
--- a/xen/common/libelf/libelf-loader.c
+++ b/xen/common/libelf/libelf-loader.c
@@ -153,7 +153,7 @@ void elf_parse_bsdsyms(struct elf_binary *elf, uint64_t
pstart)
{
uint64_t sz;
ELF_HANDLE_DECL(elf_shdr) shdr;
- unsigned i, type;
+ unsigned int i;
if ( !ELF_HANDLE_VALID(elf->sym_tab) )
return;
@@ -164,20 +164,33 @@ void elf_parse_bsdsyms(struct elf_binary *elf, uint64_t
pstart)
sz = sizeof(uint32_t);
/* Space for the elf and elf section headers */
- sz += (elf_uval(elf, elf->ehdr, e_ehsize) +
- elf_shdr_count(elf) * elf_uval(elf, elf->ehdr, e_shentsize));
+ sz += elf_uval(elf, elf->ehdr, e_ehsize) +
+ 3 * elf_uval(elf, elf->ehdr, e_shentsize);
sz = elf_round_up(elf, sz);
- /* Space for the symbol and string tables. */
+ /* Space for the symbol and string table. */
for ( i = 0; i < elf_shdr_count(elf); i++ )
{
shdr = elf_shdr_by_index(elf, i);
if ( !elf_access_ok(elf, ELF_HANDLE_PTRVAL(shdr), 1) )
/* input has an insane section header count field */
break;
- type = elf_uval(elf, shdr, sh_type);
- if ( (type == SHT_STRTAB) || (type == SHT_SYMTAB) )
- sz = elf_round_up(elf, sz + elf_uval(elf, shdr, sh_size));
+
+ if ( elf_uval(elf, shdr, sh_type) != SHT_SYMTAB )
+ continue;
+
+ sz = elf_round_up(elf, sz + elf_uval(elf, shdr, sh_size));
+ shdr = elf_shdr_by_index(elf, elf_uval(elf, shdr, sh_link));
+
+ if ( !elf_access_ok(elf, ELF_HANDLE_PTRVAL(shdr), 1) )
+ /* input has an insane section header count field */
+ break;
+
+ if ( elf_uval(elf, shdr, sh_type) != SHT_STRTAB )
+ /* Invalid symtab -> strtab link */
+ break;
+
+ sz = elf_round_up(elf, sz + elf_uval(elf, shdr, sh_size));
}
elf->bsd_symtab_pstart = pstart;
@@ -186,13 +199,31 @@ void elf_parse_bsdsyms(struct elf_binary *elf, uint64_t
pstart)
static void elf_load_bsdsyms(struct elf_binary *elf)
{
- ELF_HANDLE_DECL(elf_ehdr) sym_ehdr;
- unsigned long sz;
- elf_ptrval maxva;
- elf_ptrval symbase;
- elf_ptrval symtab_addr;
- ELF_HANDLE_DECL(elf_shdr) shdr;
- unsigned i, type;
+ /*
+ * Header that is placed at the end of the kernel and allows
+ * the OS to find where the symtab and strtab have been loaded.
+ * It mimics a valid ELF file header, although it only contains
+ * a symtab and a strtab section.
+ *
+ * NB: according to the ELF spec there's only ONE symtab per ELF
+ * file, and accordingly we will only load the corresponding
+ * strtab, so we only need three section headers in our fake ELF
+ * header (first section header is always a dummy).
+ */
+ struct __packed {
+ elf_ehdr header;
+ elf_shdr section[3];
+ } symbol_header;
+
+ ELF_HANDLE_DECL(elf_ehdr) header_handle;
+ unsigned long shdr_size;
+ uint32_t symsize;
+ ELF_HANDLE_DECL(elf_shdr) section_handle;
+ ELF_HANDLE_DECL(elf_shdr) image_handle;
+ unsigned int i, link;
+ elf_ptrval header_base;
+ elf_ptrval symtab_base;
+ elf_ptrval strtab_base;
if ( !elf->bsd_symtab_pstart )
return;
@@ -200,64 +231,136 @@ static void elf_load_bsdsyms(struct elf_binary *elf)
#define elf_hdr_elm(_elf, _hdr, _elm, _val) \
do { \
if ( elf_64bit(_elf) ) \
- elf_store_field(_elf, _hdr, e64._elm, _val); \
+ (_hdr).e64._elm = _val; \
else \
- elf_store_field(_elf, _hdr, e32._elm, _val); \
+ (_hdr).e32._elm = _val; \
} while ( 0 )
- symbase = elf_get_ptr(elf, elf->bsd_symtab_pstart);
- symtab_addr = maxva = symbase + sizeof(uint32_t);
+#define SYMTAB_INDEX 1
+#define STRTAB_INDEX 2
- /* Set up Elf header. */
- sym_ehdr = ELF_MAKE_HANDLE(elf_ehdr, symtab_addr);
- sz = elf_uval(elf, elf->ehdr, e_ehsize);
- elf_memcpy_safe(elf, ELF_HANDLE_PTRVAL(sym_ehdr),
ELF_HANDLE_PTRVAL(elf->ehdr), sz);
- maxva += sz; /* no round up */
+ /* Allow elf_memcpy_safe to write to symbol_header. */
+ elf->caller_xdest_base = &symbol_header;
+ elf->caller_xdest_size = sizeof(symbol_header);
- elf_hdr_elm(elf, sym_ehdr, e_phoff, 0);
- elf_hdr_elm(elf, sym_ehdr, e_shoff, elf_uval(elf, elf->ehdr, e_ehsize));
- elf_hdr_elm(elf, sym_ehdr, e_phentsize, 0);
- elf_hdr_elm(elf, sym_ehdr, e_phnum, 0);
-
- /* Copy Elf section headers. */
- shdr = ELF_MAKE_HANDLE(elf_shdr, maxva);
- sz = elf_shdr_count(elf) * elf_uval(elf, elf->ehdr, e_shentsize);
- elf_memcpy_safe(elf, ELF_HANDLE_PTRVAL(shdr),
- ELF_IMAGE_BASE(elf) + elf_uval(elf, elf->ehdr, e_shoff),
- sz);
- maxva = elf_round_up(elf, (unsigned long)maxva + sz);
+ /*
+ * Calculate the position of the various elements in GUEST MEMORY SPACE.
+ * This addresses MUST only be used with elf_load_image.
+ *
+ * NB: strtab_base cannot be calculated at this point because we don't
+ * know the size of the symtab yet, and the strtab will be placed after it.
+ */
+ header_base = elf_get_ptr(elf, elf->bsd_symtab_pstart) + sizeof(uint32_t);
+ symtab_base = elf_round_up(elf, header_base + sizeof(symbol_header));
+
+ /* Fill the ELF header, copied from the original ELF header. */
+ header_handle = ELF_MAKE_HANDLE(elf_ehdr,
+ ELF_REALPTR2PTRVAL(&symbol_header.header));
+ elf_memcpy_safe(elf, ELF_HANDLE_PTRVAL(header_handle),
+ ELF_HANDLE_PTRVAL(elf->ehdr),
+ elf_uval(elf, elf->ehdr, e_ehsize));
+
+ /* Set the offset to the shdr array. */
+ elf_hdr_elm(elf, symbol_header.header, e_shoff,
+ offsetof(typeof(symbol_header), section));
+
+ /* Set the right number of section headers. */
+ elf_hdr_elm(elf, symbol_header.header, e_shnum, 3);
+
+ /* Clear a couple of fields we don't use. */
+ elf_hdr_elm(elf, symbol_header.header, e_phoff, 0);
+ elf_hdr_elm(elf, symbol_header.header, e_phentsize, 0);
+ elf_hdr_elm(elf, symbol_header.header, e_phnum, 0);
+
+ /* Zero the dummy section. */
+ section_handle = ELF_MAKE_HANDLE(elf_shdr,
+ ELF_REALPTR2PTRVAL(&symbol_header.section[SHN_UNDEF]));
+ shdr_size = elf_uval(elf, elf->ehdr, e_shentsize);
+ elf_memset_safe(elf, ELF_HANDLE_PTRVAL(section_handle), 0, shdr_size);
+ /*
+ * Find the actual symtab and strtab in the ELF.
+ *
+ * The symtab section header is going to reside in section[SYMTAB_INDEX],
+ * while the corresponding strtab is going to be placed in
+ * section[STRTAB_INDEX]. sh_offset is mangled so it points to the offset
+ * where the sections are actually loaded (relative to the ELF header
+ * location).
+ */
+ section_handle = ELF_MAKE_HANDLE(elf_shdr,
+ ELF_REALPTR2PTRVAL(&symbol_header.section[SYMTAB_INDEX]));
for ( i = 0; i < elf_shdr_count(elf); i++ )
{
- elf_ptrval old_shdr_p;
- elf_ptrval new_shdr_p;
- type = elf_uval(elf, shdr, sh_type);
- if ( (type == SHT_STRTAB) || (type == SHT_SYMTAB) )
+ image_handle = elf_shdr_by_index(elf, i);
+ if ( elf_uval(elf, image_handle, sh_type) != SHT_SYMTAB )
+ continue;
+
+ elf_memcpy_safe(elf, ELF_HANDLE_PTRVAL(section_handle),
+ ELF_HANDLE_PTRVAL(image_handle),
+ shdr_size);
+
+ link = elf_uval(elf, section_handle, sh_link);
+ if ( link == SHN_UNDEF )
{
- elf_msg(elf, "%s: shdr %i at 0x%"ELF_PRPTRVAL" ->
0x%"ELF_PRPTRVAL"\n", __func__, i,
- elf_section_start(elf, shdr), maxva);
- sz = elf_uval(elf, shdr, sh_size);
- elf_memcpy_safe(elf, maxva, elf_section_start(elf, shdr), sz);
- /* Mangled to be based on ELF header location. */
- elf_hdr_elm(elf, shdr, sh_offset, maxva - symtab_addr);
- maxva = elf_round_up(elf, (unsigned long)maxva + sz);
+ elf_mark_broken(elf, "bad link in symtab");
+ break;
}
- old_shdr_p = ELF_HANDLE_PTRVAL(shdr);
- new_shdr_p = old_shdr_p + elf_uval(elf, elf->ehdr, e_shentsize);
- if ( new_shdr_p <= old_shdr_p ) /* wrapped or stuck */
+
+ /* Load symtab into guest memory. */
+ elf_load_image(elf, symtab_base, elf_section_start(elf,
section_handle),
+ elf_uval(elf, section_handle, sh_size),
+ elf_uval(elf, section_handle, sh_size));
+ elf_hdr_elm(elf, symbol_header.section[SYMTAB_INDEX], sh_offset,
+ symtab_base - header_base);
+ elf_hdr_elm(elf, symbol_header.section[SYMTAB_INDEX], sh_link,
+ STRTAB_INDEX);
+
+ /* Calculate the guest address where strtab is loaded. */
+ strtab_base = elf_round_up(elf, symtab_base +
+ elf_uval(elf, section_handle, sh_size));
+
+ /* Load strtab section header. */
+ section_handle = ELF_MAKE_HANDLE(elf_shdr,
+ ELF_REALPTR2PTRVAL(&symbol_header.section[STRTAB_INDEX]));
+ elf_memcpy_safe(elf, ELF_HANDLE_PTRVAL(section_handle),
+ ELF_HANDLE_PTRVAL(elf_shdr_by_index(elf, link)),
+ shdr_size);
+
+ if ( elf_uval(elf, section_handle, sh_type) != SHT_STRTAB )
{
- elf_mark_broken(elf, "bad section header length");
+ elf_mark_broken(elf, "strtab not found");
break;
}
- if ( !elf_access_ok(elf, new_shdr_p, 1) ) /* outside image */
- break;
- shdr = ELF_MAKE_HANDLE(elf_shdr, new_shdr_p);
+
+ /* Load strtab into guest memory. */
+ elf_load_image(elf, strtab_base, elf_section_start(elf,
section_handle),
+ elf_uval(elf, section_handle, sh_size),
+ elf_uval(elf, section_handle, sh_size));
+ elf_hdr_elm(elf, symbol_header.section[STRTAB_INDEX], sh_offset,
+ strtab_base - header_base);
+
+ /* Store the whole size (including headers and loaded sections). */
+ symsize = strtab_base + elf_uval(elf, section_handle, sh_size) -
+ header_base;
+ break;
}
- /* Write down the actual sym size. */
- elf_store_val(elf, uint32_t, symbase, maxva - symtab_addr);
+ /* Load the total size at symtab_pstart. */
+ elf_load_image(elf, elf_get_ptr(elf, elf->bsd_symtab_pstart),
+ ELF_REALPTR2PTRVAL(&symsize), sizeof(symsize),
+ sizeof(symsize));
+
+ /* Load the headers. */
+ elf_load_image(elf, header_base, ELF_REALPTR2PTRVAL(&symbol_header),
+ sizeof(symbol_header), sizeof(symbol_header));
+
+ /* Remove permissions from elf_memcpy_safe. */
+ elf->caller_xdest_base = NULL;
+ elf->caller_xdest_size = 0;
+#undef SYMTAB_INDEX
+#undef STRTAB_INDEX
#undef elf_ehdr_elm
}
--
1.9.5 (Apple Git-50.3)
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