[SLOF] [PATCH v2 1/3] elf: Implement elf_get_file_size to determine size of an ELF image
Alexey Kardashevskiy
aik at ozlabs.ru
Fri May 8 11:07:33 AEST 2020
On 02/04/2020 01:57, Stefan Berger wrote:
> From: Stefan Berger <stefanb at linux.ibm.com>
>
> Implement elf_get_file_size to determine the size of an ELF image
> that has been loaded into a buffer much larger than the actual size
> of the original file. We determine the size by searching for the
> farthest offset declared by the ELF headers.
>
> Signed-off-by: Stefan Berger <stefanb at linux.ibm.com>
> ---
> include/helpers.h | 2 ++
> include/libelf.h | 14 ++++++++++
> lib/libelf/elf.c | 26 ++++++++++++++++++
> lib/libelf/elf32.c | 68 ++++++++++++++++++++++++++++++++++++++++++++++
> lib/libelf/elf64.c | 56 ++++++++++++++++++++++++++++++++++++++
> 5 files changed, 166 insertions(+)
>
> diff --git a/include/helpers.h b/include/helpers.h
> index 47b2674..112184f 100644
> --- a/include/helpers.h
> +++ b/include/helpers.h
> @@ -51,5 +51,7 @@ extern unsigned long SLOF_get_vtpm_unit(void);
> const typeof(((type *)0)->member)* struct_ptr = (ptr); \
> (type *)((char *)struct_ptr - offset_of(type, member)); })
> #define ARRAY_SIZE(x) (sizeof(x) / sizeof(x[0]))
> +#define ROUNDUP(x,v) ((((x) + ((v) - 1)) / (v)) * (v))
> +#define MAX(x,y) ((x) > (y) ? (x) : (y))
>
> #endif
> diff --git a/include/libelf.h b/include/libelf.h
> index 5fbf279..48ff4d7 100644
> --- a/include/libelf.h
> +++ b/include/libelf.h
> @@ -96,4 +96,18 @@ void elf_relocate64(void *file_addr, signed long offset);
>
> int elf_forth_claim(void *addr, long size);
>
> +long elf_get_file_size(const void *buffer, const long buffer_size);
> +long elf_get_file_size32(const void *buffer, const long buffer_size);
> +long elf_get_file_size64(const void *buffer, const long buffer_size);
> +
> +#ifdef __BIG_ENDIAN__
> +#define elf64_to_cpu(x, ehdr) ((ehdr)->ei_data == ELFDATA2MSB ? (x) : bswap_64(x))
> +#define elf32_to_cpu(x, ehdr) ((ehdr)->ei_data == ELFDATA2MSB ? (x) : bswap_32(x))
> +#define elf16_to_cpu(x, ehdr) ((ehdr)->ei_data == ELFDATA2MSB ? (x) : bswap_16(x))
> +#else
> +#define elf64_to_cpu(x, ehdr) ((ehdr)->ei_data == ELFDATA2LSB ? (x) : bswap_64(x))
> +#define elf32_to_cpu(x, ehdr) ((ehdr)->ei_data == ELFDATA2LSB ? (x) : bswap_32(x))
> +#define elf16_to_cpu(x, ehdr) ((ehdr)->ei_data == ELFDATA2LSB ? (x) : bswap_16(x))
> +#endif
> +
> #endif /* __LIBELF_H */
> diff --git a/lib/libelf/elf.c b/lib/libelf/elf.c
> index 5204bc3..d368454 100644
> --- a/lib/libelf/elf.c
> +++ b/lib/libelf/elf.c
> @@ -196,3 +196,29 @@ elf_get_base_addr(void *file_addr)
>
> return -1;
> }
> +
> +/**
> + * Get the file size of the ELF image that has been loaded into a
> + * buffer larger than the size of the file
> + * @return The size of the ELF image or < 0 for error
> + */
> +long elf_get_file_size(const void *buffer, const long buffer_size)
> +{
> + const struct ehdr *ehdr = (const struct ehdr *)buffer;
> +
> + if (buffer_size < sizeof(struct ehdr))
> + return -1;
> +
> + /* check if it is an ELF image at all */
> + if (cpu_to_be32(ehdr->ei_ident) != 0x7f454c46)
> + return -1;
> +
> + switch (ehdr->ei_class) {
> + case 1:
> + return elf_get_file_size32(buffer, buffer_size);
> + case 2:
> + return elf_get_file_size64(buffer, buffer_size);
> + }
> +
> + return -1;
> +}
> diff --git a/lib/libelf/elf32.c b/lib/libelf/elf32.c
> index fea5cf4..7ea85f0 100644
> --- a/lib/libelf/elf32.c
> +++ b/lib/libelf/elf32.c
> @@ -17,6 +17,7 @@
> #include <string.h>
> #include <libelf.h>
> #include <byteorder.h>
> +#include <helpers.h>
>
> struct ehdr32 {
> uint32_t ei_ident;
> @@ -50,6 +51,18 @@ struct phdr32 {
> uint32_t p_align;
> };
>
> +struct shdr32 {
> + uint32_t sh_name;
> + uint32_t sh_type;
> + uint32_t sh_flags;
> + uint32_t sh_addr;
> + uint32_t sh_offset;
> + uint32_t sh_size;
> + uint32_t sh_link;
> + uint32_t sh_info;
> + uint32_t sh_addralign;
> + uint32_t sh_entsize;
> +};
>
> static struct phdr32*
> get_phdr32(void *file_addr)
> @@ -191,3 +204,58 @@ elf_byteswap_header32(void *file_addr)
> phdr = (struct phdr32 *)(((uint8_t *)phdr) + ehdr->e_phentsize);
> }
> }
> +
> +/*
> + * Determine the size of an ELF image that has been loaded into
> + * a buffer larger than its size. We search all program headers
> + * and sections for the one that shows the farthest extent of the
> + * file.
> + * @return Return -1 on error, size of file otherwise.
> + */
> +long elf_get_file_size32(const void *buffer, const long buffer_size)
> +{
> + const struct ehdr32 *ehdr = (const struct ehdr32 *) buffer;
> + const uint8_t *buffer_end = buffer + buffer_size;
> + const struct phdr32 *phdr;
> + const struct shdr32 *shdr;
> + long elf_size = -1;
> + uint16_t entsize;
> + unsigned i;
> +
> + if (buffer_size < sizeof(struct ehdr) || ehdr->e_ehsize != 52)
What is 52? sizeof(struct ehdr32)? Why "!=" rather ">=" ?
> + return -1;
> +
> + phdr = buffer + elf32_to_cpu(ehdr->e_phoff, ehdr);
> + entsize = elf16_to_cpu(ehdr->e_phentsize, ehdr);
> + for (i = 0; i < elf16_to_cpu(ehdr->e_phnum, ehdr); i++) {
> + if (((uint8_t *)phdr) + entsize > buffer_end)
> + return -1;
> +
> + elf_size = MAX(elf32_to_cpu(phdr->p_offset, ehdr) +
> + elf32_to_cpu(phdr->p_filesz, ehdr),
> + elf_size);
> +
> + /* step to next header */
> + phdr = (struct phdr32 *)(((uint8_t *)phdr) + entsize);
> + }
> +
> + shdr = buffer + elf32_to_cpu(ehdr->e_shoff, ehdr);
> + entsize = elf16_to_cpu(ehdr->e_shentsize, ehdr);
> + for (i = 0; i < elf16_to_cpu(ehdr->e_shnum, ehdr); i++) {
> + if (((uint8_t *)shdr) + entsize > buffer_end)
> + return -1;
> +
> + elf_size = MAX(elf32_to_cpu(shdr->sh_offset, ehdr) +
> + elf32_to_cpu(shdr->sh_size, ehdr),
> + elf_size);
> +
> + /* step to next header */
> + shdr = (struct shdr32 *)(((uint8_t *)shdr) + entsize);
> + }
> +
> + elf_size = ROUNDUP(elf_size, 4);
> + if (elf_size > buffer_size)
> + return -1;
> +
> + return elf_size;
> +}
> diff --git a/lib/libelf/elf64.c b/lib/libelf/elf64.c
> index 775cdee..824b56f 100644
> --- a/lib/libelf/elf64.c
> +++ b/lib/libelf/elf64.c
> @@ -20,6 +20,7 @@
> #include <stdio.h>
> #include <libelf.h>
> #include <byteorder.h>
> +#include <helpers.h>
>
> struct ehdr64
> {
> @@ -472,3 +473,58 @@ uint32_t elf_get_eflags_64(void *file_addr)
>
> return ehdr->e_flags;
> }
> +
> +/*
> + * Determine the size of an ELF image that has been loaded into
> + * a buffer larger than its size. We search all program headers
> + * and sections for the one that shows the farthest extent of the
> + * file.
> + * @return Return -1 on error, size of file otherwise.
> + */
> +long elf_get_file_size64(const void *buffer, const long buffer_size)
> +{
> + const struct ehdr64 *ehdr = (const struct ehdr64 *) buffer;
> + const uint8_t *buffer_end = buffer + buffer_size;
> + const struct phdr64 *phdr;
> + const struct shdr64 *shdr;
> + long elf_size = -1;
> + uint16_t entsize;
> + unsigned i;
> +
> + if (buffer_size < sizeof(struct ehdr) || ehdr->e_ehsize != 64)
The same questions here.
> + return -1;
> +
> + phdr = buffer + elf64_to_cpu(ehdr->e_phoff, ehdr);
> + entsize = elf16_to_cpu(ehdr->e_phentsize, ehdr);
> + for (i = 0; i < elf16_to_cpu(ehdr->e_phnum, ehdr); i++) {
> + if (((uint8_t *)phdr) + entsize > buffer_end)
> + return -1;
> +
> + elf_size = MAX(elf64_to_cpu(phdr->p_offset, ehdr) +
> + elf64_to_cpu(phdr->p_filesz, ehdr),
> + elf_size);
> +
> + /* step to next header */
> + phdr = (struct phdr64 *)(((uint8_t *)phdr) + entsize);
> + }
> +
> + shdr = buffer + elf64_to_cpu(ehdr->e_shoff, ehdr);
> + entsize = elf16_to_cpu(ehdr->e_shentsize, ehdr);
> + for (i = 0; i < elf16_to_cpu(ehdr->e_shnum, ehdr); i++) {
> + if (((uint8_t *)shdr) + entsize > buffer_end)
> + return -1;
> +
> + elf_size = MAX(elf64_to_cpu(shdr->sh_offset, ehdr) +
> + elf64_to_cpu(shdr->sh_size, ehdr),
> + elf_size);
> +
> + /* step to next header */
> + shdr = (struct shdr64 *)(((uint8_t *)shdr) + entsize);
> + }
> +
> + elf_size = ROUNDUP(elf_size, 4);
> + if (elf_size > buffer_size)
> + return -1;
> +
> + return elf_size;
> +}
>
--
Alexey
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