From 1f356e8c013f254b6471985bc929c8db1d08c44c Mon Sep 17 00:00:00 2001 From: Helge Deller Date: Wed, 2 Aug 2023 16:14:01 -0700 Subject: [PATCH] linux-user: Adjust initial brk when interpreter is close to executable MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit While we attempt to load a ET_DYN executable far away from TASK_UNMAPPED_BASE, we are not completely in control of the address space layout. If the interpreter lands close to the executable, leaving insufficient heap space, move brk. Tested-by: Helge Deller Signed-off-by: Helge Deller [rth: Re-order after ELF_ET_DYN_BASE patch so that we do not "temporarily break" tsan, and also to minimize the changes required. Remove image_info.reserve_brk as unused.] Reviewed-by: Akihiko Odaki Reviewed-by: Alex Bennée Signed-off-by: Richard Henderson --- linux-user/elfload.c | 51 +++++++++++++------------------------------- linux-user/qemu.h | 1 - 2 files changed, 15 insertions(+), 37 deletions(-) diff --git a/linux-user/elfload.c b/linux-user/elfload.c index d1b278d799..3553a3eaef 100644 --- a/linux-user/elfload.c +++ b/linux-user/elfload.c @@ -3110,27 +3110,6 @@ static void load_elf_image(const char *image_name, int image_fd, load_addr = loaddr; if (pinterp_name != NULL) { - /* - * This is the main executable. - * - * Reserve extra space for brk. - * We hold on to this space while placing the interpreter - * and the stack, lest they be placed immediately after - * the data segment and block allocation from the brk. - * - * 16MB is chosen as "large enough" without being so large as - * to allow the result to not fit with a 32-bit guest on a - * 32-bit host. However some 64 bit guests (e.g. s390x) - * attempt to place their heap further ahead and currently - * nothing stops them smashing into QEMUs address space. - */ -#if TARGET_LONG_BITS == 64 - info->reserve_brk = 32 * MiB; -#else - info->reserve_brk = 16 * MiB; -#endif - hiaddr += info->reserve_brk; - if (ehdr->e_type == ET_EXEC) { /* * Make sure that the low address does not conflict with @@ -3221,7 +3200,8 @@ static void load_elf_image(const char *image_name, int image_fd, info->end_code = 0; info->start_data = -1; info->end_data = 0; - info->brk = 0; + /* Usual start for brk is after all sections of the main executable. */ + info->brk = TARGET_PAGE_ALIGN(hiaddr); info->elf_flags = ehdr->e_flags; prot_exec = PROT_EXEC; @@ -3315,9 +3295,6 @@ static void load_elf_image(const char *image_name, int image_fd, info->end_data = vaddr_ef; } } - if (vaddr_em > info->brk) { - info->brk = vaddr_em; - } #ifdef TARGET_MIPS } else if (eppnt->p_type == PT_MIPS_ABIFLAGS) { Mips_elf_abiflags_v0 abiflags; @@ -3646,6 +3623,19 @@ int load_elf_binary(struct linux_binprm *bprm, struct image_info *info) if (elf_interpreter) { load_elf_interp(elf_interpreter, &interp_info, bprm->buf); + /* + * While unusual because of ELF_ET_DYN_BASE, if we are unlucky + * with the mappings the interpreter can be loaded above but + * near the main executable, which can leave very little room + * for the heap. + * If the current brk has less than 16MB, use the end of the + * interpreter. + */ + if (interp_info.brk > info->brk && + interp_info.load_bias - info->brk < 16 * MiB) { + info->brk = interp_info.brk; + } + /* If the program interpreter is one of these two, then assume an iBCS2 image. Otherwise assume a native linux image. */ @@ -3699,17 +3689,6 @@ int load_elf_binary(struct linux_binprm *bprm, struct image_info *info) bprm->core_dump = &elf_core_dump; #endif - /* - * If we reserved extra space for brk, release it now. - * The implementation of do_brk in syscalls.c expects to be able - * to mmap pages in this space. - */ - if (info->reserve_brk) { - abi_ulong start_brk = TARGET_PAGE_ALIGN(info->brk); - abi_ulong end_brk = TARGET_PAGE_ALIGN(info->brk + info->reserve_brk); - target_munmap(start_brk, end_brk - start_brk); - } - return 0; } diff --git a/linux-user/qemu.h b/linux-user/qemu.h index 2046a23037..4f8b55e2fb 100644 --- a/linux-user/qemu.h +++ b/linux-user/qemu.h @@ -30,7 +30,6 @@ struct image_info { abi_ulong start_data; abi_ulong end_data; abi_ulong brk; - abi_ulong reserve_brk; abi_ulong start_mmap; abi_ulong start_stack; abi_ulong stack_limit;