Add support for applying dynamic relocations to ELF binaries. This allows loading ET_DYN (position-independent) binaries and ET_EXEC binaries at custom load addresses.
Key changes: - Add elf_image.reloc_offset to track offset between vaddr and load address - Implement elf_compute_load_offset() to calculate relocation offset - Add elf_set_load_address() API to specify custom load address - Implement elf_find_dynamic_segment() to locate PT_DYNAMIC - Add elf_relocate() to apply relocations - Provide weak default elf_apply_relocations() stub for unsupported architectures - Add ELF dynamic section accessors The relocation offset type is unsigned long to properly handle pointer arithmetic and avoid casting issues. Architecture-specific implementations should override the weak elf_apply_relocations() function to handle their relocation types. Signed-off-by: Sascha Hauer <[email protected]> Co-Authored-By: Claude Sonnet 4.5 <[email protected]> --- common/elf.c | 187 ++++++++++++++++++++++++++++++++++++++++++++++++++++++-- include/elf.h | 53 ++++++++++++++++ lib/Makefile | 1 + lib/elf_reloc.c | 15 +++++ 4 files changed, 251 insertions(+), 5 deletions(-) diff --git a/common/elf.c b/common/elf.c index 692323c6beab2dd8aae9a9e874fb4980152a74e0..fc2949c285ebb0c0740c68c551926da8d0bb8637 100644 --- a/common/elf.c +++ b/common/elf.c @@ -65,9 +65,63 @@ static void elf_release_regions(struct elf_image *elf) } } +static int elf_compute_load_offset(struct elf_image *elf) +{ + void *buf = elf->hdr_buf; + void *phdr = buf + elf_hdr_e_phoff(elf, buf); + u64 min_vaddr = (u64)-1; + u64 min_paddr = (u64)-1; + int i; + + /* Find lowest p_vaddr and p_paddr in PT_LOAD segments */ + for (i = 0; i < elf_hdr_e_phnum(elf, buf); i++) { + if (elf_phdr_p_type(elf, phdr) == PT_LOAD) { + u64 vaddr = elf_phdr_p_vaddr(elf, phdr); + u64 paddr = elf_phdr_p_paddr(elf, phdr); + + if (vaddr < min_vaddr) + min_vaddr = vaddr; + if (paddr < min_paddr) + min_paddr = paddr; + } + phdr += elf_size_of_phdr(elf); + } + + /* + * Determine base load address: + * 1. If user specified load_address, use it + * 2. Otherwise for ET_EXEC, use NULL (segments use p_paddr directly) + * 3. For ET_DYN, use lowest p_paddr + */ + if (elf->load_address) { + elf->base_load_addr = elf->load_address; + } else if (elf->type == ET_EXEC) { + elf->base_load_addr = NULL; + } else { + elf->base_load_addr = (void *)(phys_addr_t)min_paddr; + } + + /* + * Calculate relocation offset: + * - For ET_EXEC with no custom load address: no offset needed + * - Otherwise: offset = base_load_addr - lowest_vaddr + */ + if (elf->type == ET_EXEC && !elf->load_address) { + elf->reloc_offset = 0; + } else { + elf->reloc_offset = ((unsigned long)elf->base_load_addr - min_vaddr); + } + + pr_debug("ELF load: type=%s, base=%p, offset=%08lx\n", + elf->type == ET_EXEC ? "ET_EXEC" : "ET_DYN", + elf->base_load_addr, elf->reloc_offset); + + return 0; +} + static int request_elf_segment(struct elf_image *elf, void *phdr) { - void *dst = (void *) (phys_addr_t) elf_phdr_p_paddr(elf, phdr); + void *dst; int ret; u64 p_memsz = elf_phdr_p_memsz(elf, phdr); @@ -78,6 +132,20 @@ static int request_elf_segment(struct elf_image *elf, void *phdr) if (!p_memsz) return 0; + /* + * Calculate destination address: + * - If reloc_offset is set (custom load address or ET_DYN): + * dst = reloc_offset + p_vaddr + * - Otherwise (ET_EXEC, no custom address): + * dst = p_paddr (original behavior) + */ + if (elf->reloc_offset) { + u64 p_vaddr = elf_phdr_p_vaddr(elf, phdr); + dst = (void *)(unsigned long)(elf->reloc_offset + p_vaddr); + } else { + dst = (void *)(unsigned long)elf_phdr_p_paddr(elf, phdr); + } + if (dst < elf->low_addr) elf->low_addr = dst; if (dst + p_memsz > elf->high_addr) @@ -129,7 +197,18 @@ static int load_elf_to_memory(struct elf_image *elf) p_offset = elf_phdr_p_offset(elf, r->phdr); p_filesz = elf_phdr_p_filesz(elf, r->phdr); p_memsz = elf_phdr_p_memsz(elf, r->phdr); - dst = (void *) (phys_addr_t) elf_phdr_p_paddr(elf, r->phdr); + + /* + * Calculate destination address (same logic as request_elf_segment): + * - If reloc_offset is set: dst = reloc_offset + p_vaddr + * - Otherwise: dst = p_paddr + */ + if (elf->reloc_offset) { + u64 p_vaddr = elf_phdr_p_vaddr(elf, r->phdr); + dst = (void *)(unsigned long)(elf->reloc_offset + p_vaddr); + } else { + dst = (void *)(unsigned long)elf_phdr_p_paddr(elf, r->phdr); + } pr_debug("Loading phdr offset 0x%llx to 0x%p (%llu bytes)\n", p_offset, dst, p_filesz); @@ -173,6 +252,11 @@ static int load_elf_image_segments(struct elf_image *elf) if (!list_empty(&elf->list)) return -EINVAL; + /* Calculate load offset for ET_DYN */ + ret = elf_compute_load_offset(elf); + if (ret) + return ret; + for (i = 0; i < elf_hdr_e_phnum(elf, buf) ; ++i) { ret = request_elf_segment(elf, phdr); if (ret) @@ -201,6 +285,8 @@ static int load_elf_image_segments(struct elf_image *elf) static int elf_check_image(struct elf_image *elf, void *buf) { + u16 e_type; + if (memcmp(buf, ELFMAG, SELFMAG)) { pr_err("ELF magic not found.\n"); return -EINVAL; @@ -208,11 +294,14 @@ static int elf_check_image(struct elf_image *elf, void *buf) elf->class = ((char *) buf)[EI_CLASS]; - if (elf_hdr_e_type(elf, buf) != ET_EXEC) { - pr_err("Non EXEC ELF image.\n"); + e_type = elf_hdr_e_type(elf, buf); + if (e_type != ET_EXEC && e_type != ET_DYN) { + pr_err("Unsupported ELF type: %u (only ET_EXEC and ET_DYN supported)\n", e_type); return -ENOEXEC; } + elf->type = e_type; + if (!elf_hdr_e_phnum(elf, buf)) { pr_err("No phdr found.\n"); return -ENOEXEC; @@ -338,9 +427,97 @@ struct elf_image *elf_open(const char *filename) return elf_check_init(filename); } +void elf_set_load_address(struct elf_image *elf, void *addr) +{ + elf->load_address = addr; +} + +static void *elf_find_dynamic_segment(struct elf_image *elf) +{ + void *buf = elf->hdr_buf; + void *phdr = buf + elf_hdr_e_phoff(elf, buf); + int i; + + for (i = 0; i < elf_hdr_e_phnum(elf, buf); i++) { + if (elf_phdr_p_type(elf, phdr) == PT_DYNAMIC) { + u64 offset = elf_phdr_p_offset(elf, phdr); + void *dyn_addr; + + /* If loaded from file, PT_DYNAMIC might not be in hdr_buf */ + if (elf->filename) { + /* + * Calculate address in loaded memory using same logic + * as request_elf_segment + */ + if (elf->reloc_offset) { + u64 p_vaddr = elf_phdr_p_vaddr(elf, phdr); + dyn_addr = (void *)(unsigned long)(elf->reloc_offset + p_vaddr); + } else { + u64 paddr = elf_phdr_p_paddr(elf, phdr); + dyn_addr = (void *)(phys_addr_t)paddr; + } + return dyn_addr; + } else { + /* Binary in memory, use offset */ + return elf->hdr_buf + offset; + } + } + phdr += elf_size_of_phdr(elf); + } + + return NULL; /* No PT_DYNAMIC segment */ +} + +static int elf_relocate(struct elf_image *elf) +{ + void *dyn_seg; + + /* + * Relocations needed if: + * - ET_DYN (position-independent), OR + * - ET_EXEC with custom load address + */ + if (elf->type == ET_EXEC && !elf->load_address) + return 0; + + /* Find PT_DYNAMIC segment */ + dyn_seg = elf_find_dynamic_segment(elf); + if (!dyn_seg) { + /* + * No PT_DYNAMIC segment found. + * For ET_DYN this is unusual but legal. + * For ET_EXEC with custom load address, this means no relocations + * can be applied - warn the user. + */ + if (elf->type == ET_EXEC && elf->load_address) { + pr_warn("ET_EXEC loaded at custom address but no PT_DYNAMIC segment - " + "relocations cannot be applied\n"); + } else { + pr_debug("No PT_DYNAMIC segment found\n"); + } + return 0; + } + + /* Call architecture-specific relocation handler */ + return elf_apply_relocations(elf, dyn_seg); +} + int elf_load(struct elf_image *elf) { - return load_elf_image_segments(elf); + int ret; + + ret = load_elf_image_segments(elf); + if (ret) + return ret; + + /* Apply relocations if needed */ + ret = elf_relocate(elf); + if (ret) { + pr_err("Relocation failed: %d\n", ret); + return ret; + } + + return 0; } void elf_close(struct elf_image *elf) diff --git a/include/elf.h b/include/elf.h index 994db642b0789942530f6ef7fdffdd2218afd7b6..4b19c917639d0d655d9f7530f0311afa599f1a98 100644 --- a/include/elf.h +++ b/include/elf.h @@ -394,11 +394,15 @@ extern Elf64_Dyn _DYNAMIC []; struct elf_image { struct list_head list; u8 class; + u16 type; /* ET_EXEC or ET_DYN */ u64 entry; void *low_addr; void *high_addr; void *hdr_buf; const char *filename; + void *load_address; /* User-specified load address (NULL = use p_paddr) */ + void *base_load_addr; /* Calculated base address for ET_DYN */ + unsigned long reloc_offset; /* Offset between p_vaddr and actual load address */ }; static inline size_t elf_get_mem_size(struct elf_image *elf) @@ -411,6 +415,20 @@ struct elf_image *elf_open(const char *filename); void elf_close(struct elf_image *elf); int elf_load(struct elf_image *elf); +/* + * Set the load address for the ELF file. + * Must be called before elf_load(). + * If not set, ET_EXEC uses p_paddr, ET_DYN uses lowest p_paddr. + */ +void elf_set_load_address(struct elf_image *elf, void *addr); + +/* + * Architecture-specific relocation handler. + * Returns 0 on success, -ENOSYS if architecture doesn't support relocations, + * other negative error codes on failure. + */ +int elf_apply_relocations(struct elf_image *elf, void *dyn_seg); + #define ELF_GET_FIELD(__s, __field, __type) \ static inline __type elf_##__s##_##__field(struct elf_image *elf, void *arg) { \ if (elf->class == ELFCLASS32) \ @@ -426,10 +444,12 @@ ELF_GET_FIELD(hdr, e_phentsize, u16) ELF_GET_FIELD(hdr, e_type, u16) ELF_GET_FIELD(hdr, e_machine, u16) ELF_GET_FIELD(phdr, p_paddr, u64) +ELF_GET_FIELD(phdr, p_vaddr, u64) ELF_GET_FIELD(phdr, p_filesz, u64) ELF_GET_FIELD(phdr, p_memsz, u64) ELF_GET_FIELD(phdr, p_type, u32) ELF_GET_FIELD(phdr, p_offset, u64) +ELF_GET_FIELD(phdr, p_flags, u32) static inline unsigned long elf_size_of_phdr(struct elf_image *elf) { @@ -439,4 +459,37 @@ static inline unsigned long elf_size_of_phdr(struct elf_image *elf) return sizeof(Elf64_Phdr); } +/* Dynamic section accessors */ +static inline s64 elf_dyn_d_tag(struct elf_image *elf, void *arg) +{ + if (elf->class == ELFCLASS32) + return (s64)((Elf32_Dyn *)arg)->d_tag; + else + return (s64)((Elf64_Dyn *)arg)->d_tag; +} + +static inline u64 elf_dyn_d_val(struct elf_image *elf, void *arg) +{ + if (elf->class == ELFCLASS32) + return (u64)((Elf32_Dyn *)arg)->d_un.d_val; + else + return (u64)((Elf64_Dyn *)arg)->d_un.d_val; +} + +static inline u64 elf_dyn_d_ptr(struct elf_image *elf, void *arg) +{ + if (elf->class == ELFCLASS32) + return (u64)((Elf32_Dyn *)arg)->d_un.d_ptr; + else + return (u64)((Elf64_Dyn *)arg)->d_un.d_ptr; +} + +static inline unsigned long elf_size_of_dyn(struct elf_image *elf) +{ + if (elf->class == ELFCLASS32) + return sizeof(Elf32_Dyn); + else + return sizeof(Elf64_Dyn); +} + #endif /* _LINUX_ELF_H */ diff --git a/lib/Makefile b/lib/Makefile index 9ab4cad0359c0e8e5ad0c0785d8f45afc9c1d00e..11716ec420cb46799b56512429afdbf1c2bba7cc 100644 --- a/lib/Makefile +++ b/lib/Makefile @@ -24,6 +24,7 @@ obj-y += readkey.o obj-y += kfifo.o obj-y += libbb.o obj-y += libgen.o +obj-y += elf_reloc.o obj-$(CONFIG_FIP) += fip.o tbbr_config.o obj-$(CONFIG_JSMN) += jsmn.o obj-y += stringlist.o diff --git a/lib/elf_reloc.c b/lib/elf_reloc.c new file mode 100644 index 0000000000000000000000000000000000000000..d9e09800a6a836e7a97f5d55a8120b2632c0c25e --- /dev/null +++ b/lib/elf_reloc.c @@ -0,0 +1,15 @@ +// SPDX-License-Identifier: GPL-2.0 + +#include <common.h> +#include <elf.h> +#include <errno.h> + +/* + * Weak default implementation for architectures that don't support + * ELF relocations yet. Can be overridden by arch-specific implementation. + */ +int __weak elf_apply_relocations(struct elf_image *elf, void *dyn_seg) +{ + pr_warn("ELF relocations not supported for this architecture\n"); + return -ENOSYS; +} -- 2.47.3
