Re: [PATCH v2 38/43] bsd-user: Refactor load_elf_sections and is_target_elf_binary

[Warner Losh]

> On Aug 26, 2021, at 3:11 PM, imp@bsdimp.com wrote:
> 
> From: Warner Losh <imp@FreeBSD.org>
> 
> Factor out load_elf_sections and is_target_elf_binary out of
> load_elf_interp.
> 
> Signed-off-by: Mikaël Urankar <mikael.urankar@gmail.com>
> Signed-off-by: Stacey Son <sson@FreeBSD.org>
> Signed-off-by: Warner Losh <imp@bsdimp.com>
> ---
> bsd-user/elfload.c | 350 +++++++++++++++++++++------------------------
> 1 file changed, 164 insertions(+), 186 deletions(-)
> 
> diff --git a/bsd-user/elfload.c b/bsd-user/elfload.c
> index bdf18f3dce..aed28f2f73 100644
> --- a/bsd-user/elfload.c
> +++ b/bsd-user/elfload.c
> @@ -36,6 +36,8 @@ abi_ulong target_stksiz;
> abi_ulong target_stkbas;
> 
> static int elf_core_dump(int signr, CPUArchState *env);
> +static int load_elf_sections(const struct elfhdr *hdr, struct elf_phdr *phdr,
> +    int fd, abi_ulong rbase, abi_ulong *baddrp);
> 
> static inline void memcpy_fromfs(void *to, const void *from, unsigned long n)
> {
> @@ -271,16 +273,10 @@ static abi_ulong load_elf_interp(struct elfhdr 
> *interp_elf_ex,
>                                  abi_ulong *interp_load_addr)
> {
>     struct elf_phdr *elf_phdata  =  NULL;
> -    struct elf_phdr *eppnt;
> -    abi_ulong load_addr = 0;
> -    int load_addr_set = 0;
> +    abi_ulong rbase;
>     int retval;
> -    abi_ulong last_bss, elf_bss;
> -    abi_ulong error;
> -    int i;
> +    abi_ulong baddr, error;
> 
> -    elf_bss = 0;
> -    last_bss = 0;
>     error = 0;
> 
>     bswap_ehdr(interp_elf_ex);
> @@ -325,6 +321,7 @@ static abi_ulong load_elf_interp(struct elfhdr 
> *interp_elf_ex,
>     }
>     bswap_phdr(elf_phdata, interp_elf_ex->e_phnum);
> 
> +    rbase = 0;
>     if (interp_elf_ex->e_type == ET_DYN) {
>         /*
>          * In order to avoid hardcoding the interpreter load
> @@ -332,86 +329,25 @@ static abi_ulong load_elf_interp(struct elfhdr 
> *interp_elf_ex,
>          */
>         error = target_mmap(0, INTERP_MAP_SIZE, PROT_NONE,
>                 MAP_PRIVATE | MAP_ANON, -1, 0);

s/error = /rbase = /

so that the test below worked properly.

> -        if (error == -1) {
> +        if (rbase == -1) {
>             perror("mmap");
>             exit(-1);
>         }
> -        load_addr = error;
> -        load_addr_set = 1;
> -    }
> -
> -    eppnt = elf_phdata;
> -    for (i = 0; i < interp_elf_ex->e_phnum; i++, eppnt++)
> -        if (eppnt->p_type == PT_LOAD) {
> -            int elf_type = MAP_PRIVATE | MAP_DENYWRITE;
> -            int elf_prot = 0;
> -            abi_ulong vaddr = 0;
> -            abi_ulong k;
> -
> -            if (eppnt->p_flags & PF_R) elf_prot =  PROT_READ;
> -            if (eppnt->p_flags & PF_W) elf_prot |= PROT_WRITE;
> -            if (eppnt->p_flags & PF_X) elf_prot |= PROT_EXEC;
> -            if (interp_elf_ex->e_type == ET_EXEC || load_addr_set) {
> -                elf_type |= MAP_FIXED;
> -                vaddr = eppnt->p_vaddr;
> -            }
> -            error = target_mmap(load_addr + TARGET_ELF_PAGESTART(vaddr),
> -                                eppnt->p_filesz + 
> TARGET_ELF_PAGEOFFSET(eppnt->p_vaddr),
> -                                elf_prot,
> -                                elf_type,
> -                                interpreter_fd,
> -                                eppnt->p_offset - 
> TARGET_ELF_PAGEOFFSET(eppnt->p_vaddr));
> -
> -            if (error == -1) {
> -                /* Real error */
> -                close(interpreter_fd);
> -                free(elf_phdata);
> -                return ~((abi_ulong)0UL);
> -            }
> -
> -            if (!load_addr_set && interp_elf_ex->e_type == ET_DYN) {
> -                load_addr = error;
> -                load_addr_set = 1;
> -            }
> -
> -            /*
> -             * Find the end of the file  mapping for this phdr, and keep
> -             * track of the largest address we see for this.
> -             */
> -            k = load_addr + eppnt->p_vaddr + eppnt->p_filesz;
> -            if (k > elf_bss) elf_bss = k;
> +    }
> 
> -            /*
> -             * Do the same thing for the memory mapping - between
> -             * elf_bss and last_bss is the bss section.
> -             */
> -            k = load_addr + eppnt->p_memsz + eppnt->p_vaddr;
> -            if (k > last_bss) last_bss = k;
> -        }
> +    error = load_elf_sections(interp_elf_ex, elf_phdata, interpreter_fd, 
> rbase,
> +        &baddr);
> +    if (error != 0) {
> +        perror("load_elf_sections");
> +        exit(-1);
> +    }
> 
>     /* Now use mmap to map the library into memory. */
> -
>     close(interpreter_fd);
> -
> -    /*
> -     * Now fill out the bss section.  First pad the last page up
> -     * to the page boundary, and then perform a mmap to make sure
> -     * that there are zeromapped pages up to and including the last
> -     * bss page.
> -     */
> -    padzero(elf_bss, last_bss);
> -    elf_bss = TARGET_ELF_PAGESTART(elf_bss + qemu_host_page_size - 1); /* 
> What we have mapped so far */
> -
> -    /* Map the last of the bss segment */
> -    if (last_bss > elf_bss) {
> -        target_mmap(elf_bss, last_bss - elf_bss,
> -                    PROT_READ | PROT_WRITE | PROT_EXEC,
> -                    MAP_FIXED | MAP_PRIVATE | MAP_ANON, -1, 0);
> -    }
>     free(elf_phdata);
> 
> -    *interp_load_addr = load_addr;
> -    return ((abi_ulong) interp_elf_ex->e_entry) + load_addr;
> +    *interp_load_addr = baddr;
> +    return ((abi_ulong) interp_elf_ex->e_entry) + rbase;
> }
> 
> static int symfind(const void *s0, const void *s1)
> @@ -521,6 +457,10 @@ found:
>             }
>             continue;
>         }
> +#if defined(TARGET_ARM) || defined(TARGET_MIPS)
> +        /* The bottom address bit marks a Thumb or MIPS16 symbol.  */
> +        syms[i].st_value &= ~(target_ulong)1;
> +#endif
>         i++;
>     }
> 
> @@ -560,26 +500,119 @@ found:
>     syminfos = s;
> }
> 
> +/* Check the elf header and see if this a target elf binary. */
> +int is_target_elf_binary(int fd)
> +{
> +    uint8_t buf[128];
> +    struct elfhdr elf_ex;
> +
> +    if (lseek(fd, 0L, SEEK_SET) < 0) {
> +        return 0;
> +    }
> +    if (read(fd, buf, sizeof(buf)) < 0) {
> +        return 0;
> +    }
> +
> +    elf_ex = *((struct elfhdr *)buf);
> +    bswap_ehdr(&elf_ex);
> +
> +    if ((elf_ex.e_type != ET_EXEC && elf_ex.e_type != ET_DYN) ||
> +        (!elf_check_arch(elf_ex.e_machine))) {
> +        return 0;
> +    } else {
> +        return 1;
> +    }
> +}
> +
> +static int
> +load_elf_sections(const struct elfhdr *hdr, struct elf_phdr *phdr, int fd,
> +    abi_ulong rbase, abi_ulong *baddrp)
> +{
> +    struct elf_phdr *elf_ppnt;
> +    abi_ulong baddr;
> +    int i;
> +    bool first;
> +
> +    /*
> +     * Now we do a little grungy work by mmaping the ELF image into
> +     * the correct location in memory.  At this point, we assume that
> +     * the image should be loaded at fixed address, not at a variable
> +     * address.
> +     */
> +    first = true;
> +    for (i = 0, elf_ppnt = phdr; i < hdr->e_phnum; i++, elf_ppnt++) {
> +        int elf_prot = 0;
> +        abi_ulong error;
> +
> +        /* XXX Skip memsz == 0. */
> +        if (elf_ppnt->p_type != PT_LOAD) {
> +            continue;
> +        }
> +
> +        if (elf_ppnt->p_flags & PF_R) {
> +            elf_prot |= PROT_READ;
> +        }
> +        if (elf_ppnt->p_flags & PF_W) {
> +            elf_prot |= PROT_WRITE;
> +        }
> +        if (elf_ppnt->p_flags & PF_X) {
> +            elf_prot |= PROT_EXEC;
> +        }
> +
> +        error = target_mmap(TARGET_ELF_PAGESTART(rbase + elf_ppnt->p_vaddr),
> +                            (elf_ppnt->p_filesz +
> +                             TARGET_ELF_PAGEOFFSET(elf_ppnt->p_vaddr)),
> +                            elf_prot,
> +                            (MAP_FIXED | MAP_PRIVATE | MAP_DENYWRITE),
> +                            fd,
> +                            (elf_ppnt->p_offset -
> +                             TARGET_ELF_PAGEOFFSET(elf_ppnt->p_vaddr)));
> +        if (error == -1) {
> +            perror("mmap");
> +            exit(-1);
> +        } else if (elf_ppnt->p_memsz != elf_ppnt->p_filesz) {
> +            abi_ulong start_bss, end_bss;
> +
> +            start_bss = rbase + elf_ppnt->p_vaddr + elf_ppnt->p_filesz;
> +            end_bss = rbase + elf_ppnt->p_vaddr + elf_ppnt->p_memsz;
> +
> +            /*
> +             * Calling set_brk effectively mmaps the pages that we need for 
> the
> +             * bss and break sections.
> +             */
> +            set_brk(start_bss, end_bss);
> +            padzero(start_bss, end_bss);
> +        }
> +
> +        if (first) {
> +            baddr = TARGET_ELF_PAGESTART(rbase + elf_ppnt->p_vaddr);
> +            first = false;
> +        }
> +    }
> +
> +    if (baddrp != NULL) {
> +        *baddrp = baddr;
> +    }
> +    return 0;
> +}
> +
> int load_elf_binary(struct bsd_binprm *bprm, struct target_pt_regs *regs,
>                     struct image_info *info)
> {
>     struct elfhdr elf_ex;
>     struct elfhdr interp_elf_ex;
>     int interpreter_fd = -1; /* avoid warning */
> -    abi_ulong load_addr, load_bias;
> -    int load_addr_set = 0;
> +    abi_ulong load_addr;
>     int i;
> -    struct elf_phdr * elf_ppnt;
> +    struct elf_phdr *elf_ppnt;
>     struct elf_phdr *elf_phdata;
> -    abi_ulong elf_bss, k, elf_brk;
> -    int retval;
> -    char * elf_interpreter;
> -    abi_ulong elf_entry, interp_load_addr = 0;
> -    abi_ulong start_code, end_code, start_data, end_data;
> +    abi_ulong elf_brk;
> +    int error, retval;
> +    char *elf_interpreter;
> +    abi_ulong baddr, elf_entry, et_dyn_addr, interp_load_addr = 0;
>     abi_ulong reloc_func_desc = 0;
> 
>     load_addr = 0;
> -    load_bias = 0;
>     elf_ex = *((struct elfhdr *) bprm->buf);          /* exec-header */
>     bswap_ehdr(&elf_ex);
> 
> @@ -618,16 +651,10 @@ int load_elf_binary(struct bsd_binprm *bprm, struct 
> target_pt_regs *regs,
>     bswap_phdr(elf_phdata, elf_ex.e_phnum);
>     elf_ppnt = elf_phdata;
> 
> -    elf_bss = 0;
>     elf_brk = 0;
> 
> 
>     elf_interpreter = NULL;
> -    start_code = ~((abi_ulong)0UL);
> -    end_code = 0;
> -    start_data = 0;
> -    end_data = 0;
> -
>     for (i = 0; i < elf_ex.e_phnum; i++) {
>         if (elf_ppnt->p_type == PT_INTERP) {
>             if (elf_interpreter != NULL) {
> @@ -714,94 +741,45 @@ int load_elf_binary(struct bsd_binprm *bprm, struct 
> target_pt_regs *regs,
>     info->mmap = 0;
>     elf_entry = (abi_ulong) elf_ex.e_entry;
> 
> -    /* Do this so that we can load the interpreter, if need be.  We will
> -       change some of these later */
> +    /* XXX Join this with PT_INTERP search? */
> +    baddr = 0;
> +    for (i = 0, elf_ppnt = elf_phdata; i < elf_ex.e_phnum; i++, elf_ppnt++) {
> +        if (elf_ppnt->p_type != PT_LOAD) {
> +            continue;
> +        }
> +        baddr = elf_ppnt->p_vaddr;
> +        break;
> +    }
> +
> +    et_dyn_addr = 0;
> +    if (elf_ex.e_type == ET_DYN && baddr == 0) {
> +        et_dyn_addr = ELF_ET_DYN_LOAD_ADDR;
> +    }
> +
> +    /*
> +     * Do this so that we can load the interpreter, if need be.  We will
> +     * change some of these later
> +     */
>     info->rss = 0;
>     setup_arg_pages(bprm, info, &bprm->p, &bprm->stringp);
>     info->start_stack = bprm->p;
> 
> -    /* Now we do a little grungy work by mmaping the ELF image into
> -     * the correct location in memory.  At this point, we assume that
> -     * the image should be loaded at fixed address, not at a variable
> -     * address.
> -     */
> +    info->elf_flags = elf_ex.e_flags;
> 
> +    error = load_elf_sections(&elf_ex, elf_phdata, bprm->fd, et_dyn_addr,
> +        &load_addr);
>     for (i = 0, elf_ppnt = elf_phdata; i < elf_ex.e_phnum; i++, elf_ppnt++) {
> -        int elf_prot = 0;
> -        int elf_flags = 0;
> -        abi_ulong error;
> -
> -        if (elf_ppnt->p_type != PT_LOAD)
> +        if (elf_ppnt->p_type != PT_LOAD) {
>             continue;
> -
> -        if (elf_ppnt->p_flags & PF_R) elf_prot |= PROT_READ;
> -        if (elf_ppnt->p_flags & PF_W) elf_prot |= PROT_WRITE;
> -        if (elf_ppnt->p_flags & PF_X) elf_prot |= PROT_EXEC;
> -        elf_flags = MAP_PRIVATE | MAP_DENYWRITE;
> -        if (elf_ex.e_type == ET_EXEC || load_addr_set) {
> -            elf_flags |= MAP_FIXED;
> -        } else if (elf_ex.e_type == ET_DYN) {
> -            /* Try and get dynamic programs out of the way of the default 
> mmap
> -               base, as well as whatever program they might try to exec.  
> This
> -               is because the brk will follow the loader, and is not 
> movable.  */
> -            /* NOTE: for qemu, we do a big mmap to get enough space
> -               without hardcoding any address */
> -            error = target_mmap(0, ET_DYN_MAP_SIZE,
> -                                PROT_NONE, MAP_PRIVATE | MAP_ANON,
> -                                -1, 0);
> -            if (error == -1) {
> -                perror("mmap");
> -                exit(-1);
> -            }
> -            load_bias = TARGET_ELF_PAGESTART(error - elf_ppnt->p_vaddr);
>         }
> -
> -        error = target_mmap(TARGET_ELF_PAGESTART(load_bias + 
> elf_ppnt->p_vaddr),
> -                            (elf_ppnt->p_filesz +
> -                             TARGET_ELF_PAGEOFFSET(elf_ppnt->p_vaddr)),
> -                            elf_prot,
> -                            (MAP_FIXED | MAP_PRIVATE | MAP_DENYWRITE),
> -                            bprm->fd,
> -                            (elf_ppnt->p_offset -
> -                             TARGET_ELF_PAGEOFFSET(elf_ppnt->p_vaddr)));
> -        if (error == -1) {
> -            perror("mmap");
> -            exit(-1);
> -        }
> -
> -        if (!load_addr_set) {
> -            load_addr_set = 1;
> -            load_addr = elf_ppnt->p_vaddr - elf_ppnt->p_offset;
> -            if (elf_ex.e_type == ET_DYN) {
> -                load_bias += error -
> -                    TARGET_ELF_PAGESTART(load_bias + elf_ppnt->p_vaddr);
> -                load_addr += load_bias;
> -                reloc_func_desc = load_bias;
> -            }
> -        }
> -        k = elf_ppnt->p_vaddr;
> -        if (k < start_code)
> -            start_code = k;
> -        if (start_data < k)
> -            start_data = k;
> -        k = elf_ppnt->p_vaddr + elf_ppnt->p_filesz;
> -        if (k > elf_bss)
> -            elf_bss = k;
> -        if ((elf_ppnt->p_flags & PF_X) && end_code <  k)
> -            end_code = k;
> -        if (end_data < k)
> -            end_data = k;
> -        k = elf_ppnt->p_vaddr + elf_ppnt->p_memsz;
> -        if (k > elf_brk) elf_brk = k;
> -    }
> -
> -    elf_entry += load_bias;
> -    elf_bss += load_bias;
> -    elf_brk += load_bias;
> -    start_code += load_bias;
> -    end_code += load_bias;
> -    start_data += load_bias;
> -    end_data += load_bias;
> +        if (elf_ppnt->p_memsz > elf_ppnt->p_filesz)
> +            elf_brk = MAX(elf_brk, et_dyn_addr + elf_ppnt->p_vaddr +
> +                elf_ppnt->p_memsz);
> +    }
> +    if (error != 0) {
> +        perror("load_elf_sections");
> +        exit(-1);
> +    }
> 
>     if (elf_interpreter) {
>         elf_entry = load_elf_interp(&interp_elf_ex, interpreter_fd,
> @@ -817,6 +795,9 @@ int load_elf_binary(struct bsd_binprm *bprm, struct 
> target_pt_regs *regs,
>             exit(-1);
>             return 0;
>         }
> +    } else {
> +        interp_load_addr = et_dyn_addr;
> +        elf_entry += interp_load_addr;
>     }
> 
>     free(elf_phdata);
> @@ -827,21 +808,18 @@ int load_elf_binary(struct bsd_binprm *bprm, struct 
> target_pt_regs *regs,
> 
>     close(bprm->fd);
> 
> -    bprm->p = target_create_elf_tables(bprm->p, bprm->argc, bprm->envc, 
> bprm->stringp,
> -                                       &elf_ex, load_addr, load_bias, 
> interp_load_addr, info);
> +    bprm->p = target_create_elf_tables(bprm->p,
> +                    bprm->argc,
> +                    bprm->envc,
> +                    bprm->stringp,
> +                    &elf_ex,
> +                    load_addr, et_dyn_addr,
> +                    interp_load_addr,
> +                    info);
>     info->load_addr = reloc_func_desc;
>     info->start_brk = info->brk = elf_brk;
> -    info->end_code = end_code;
> -    info->start_code = start_code;
> -    info->start_data = start_data;
> -    info->end_data = end_data;
>     info->start_stack = bprm->p;
> -
> -    /* Calling set_brk effectively mmaps the pages that we need for the bss 
> and break
> -       sections */
> -    set_brk(elf_bss, elf_brk);
> -
> -    padzero(elf_bss, elf_brk);
> +    info->load_bias = 0;
> 
>     info->entry = elf_entry;
> 
> --
> 2.32.0
>

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