Move complete MMU setup into PBL by leveraging ELF segment information to apply correct memory permissions before jumping to barebox proper.
After ELF relocation, parse PT_LOAD segments and map each with permissions derived from p_flags: - Text segments (PF_R|PF_X): Read-only + executable (MAP_CODE) - Data segments (PF_R|PF_W): Read-write (MAP_CACHED) - RO data segments (PF_R): Read-only (MAP_CACHED_RO) This ensures barebox proper starts with full W^X protection already in place, eliminating the need for complex remapping in barebox proper. The framework is portable - common ELF parsing in pbl/mmu.c uses architecture-specific early_remap_range() exported from mmu_*.c. Co-Authored-By: Claude Sonnet 4.5 <[email protected]> Reviewed-by: Ahmad Fatoum <[email protected]> Signed-off-by: Sascha Hauer <[email protected]> --- arch/arm/cpu/mmu-common.c | 31 +++++++------- arch/arm/cpu/uncompress.c | 10 +++++ include/pbl/mmu.h | 38 +++++++++++++++++ pbl/Makefile | 1 + pbl/mmu.c | 105 ++++++++++++++++++++++++++++++++++++++++++++++ 5 files changed, 169 insertions(+), 16 deletions(-) diff --git a/arch/arm/cpu/mmu-common.c b/arch/arm/cpu/mmu-common.c index 67317f127c..4f3ad4a794 100644 --- a/arch/arm/cpu/mmu-common.c +++ b/arch/arm/cpu/mmu-common.c @@ -109,28 +109,26 @@ static inline void remap_range_end(unsigned long start, unsigned long end, remap_range((void *)start, end - start, map_type); } -static inline void remap_range_end_sans_text(unsigned long start, unsigned long end, +static inline void remap_range_end_sans_image(unsigned long start, unsigned long end, unsigned map_type) { - unsigned long text_start = (unsigned long)&_stext; - unsigned long text_end = (unsigned long)&_etext; + unsigned long image_start = (unsigned long)&__image_start; + unsigned long image_end = (unsigned long)&__image_end; - if (region_overlap_end_exclusive(start, end, text_start, text_end)) { - remap_range_end(start, text_start, MAP_CACHED); - /* skip barebox segments here, will be mapped later */ - start = text_end; + if (region_overlap_end_exclusive(start, end, image_start, image_end)) { + remap_range_end(start, image_start, MAP_CACHED); + /* skip barebox segments here, PBL has already mapped them */ + start = image_end; } + start = ALIGN(start, PAGE_SIZE); + remap_range_end(start, end, MAP_CACHED); } static void mmu_remap_memory_banks(void) { struct memory_bank *bank; - unsigned long code_start = (unsigned long)&_stext; - unsigned long code_size = (unsigned long)&__start_rodata - (unsigned long)&_stext; - unsigned long rodata_start = (unsigned long)&__start_rodata; - unsigned long rodata_size = (unsigned long)&__end_rodata - rodata_start; /* * Early mmu init will have mapped everything but the initial memory area @@ -138,6 +136,10 @@ static void mmu_remap_memory_banks(void) * all memory banks, so let's map all pages, excluding reserved memory areas * and barebox text area cacheable. * + * PBL has already set up the MMU with proper permissions for text, data + * and rodata based on ELF segment information, so we don't need to remap + * those here. + * * This code will become much less complex once we switch over to using * CONFIG_MEMORY_ATTRIBUTES for MMU as well. */ @@ -150,16 +152,13 @@ static void mmu_remap_memory_banks(void) /* Skip reserved regions */ for_each_reserved_region(bank, rsv) { if (pos != rsv->start) - remap_range_end_sans_text(pos, rsv->start, MAP_CACHED); + remap_range_end_sans_image(pos, rsv->start, MAP_CACHED); pos = rsv->end + 1; } - remap_range_end_sans_text(pos, bank->res->end + 1, MAP_CACHED); + remap_range_end_sans_image(pos, bank->res->end + 1, MAP_CACHED); } - remap_range((void *)code_start, code_size, MAP_CODE); - remap_range((void *)rodata_start, rodata_size, MAP_CACHED_RO); - setup_trap_pages(); } diff --git a/arch/arm/cpu/uncompress.c b/arch/arm/cpu/uncompress.c index 10df5fcba9..9a9f391022 100644 --- a/arch/arm/cpu/uncompress.c +++ b/arch/arm/cpu/uncompress.c @@ -21,6 +21,7 @@ #include <asm/unaligned.h> #include <compressed-dtb.h> #include <elf.h> +#include <pbl/mmu.h> #include <debug_ll.h> @@ -103,6 +104,15 @@ void __noreturn barebox_pbl_start(unsigned long membase, unsigned long memsize, if (ret) panic("Failed to relocate ELF: %d\n", ret); + /* + * Now that the ELF image is relocated, we know the exact addresses + * of all segments. Set up MMU with proper permissions based on + * ELF segment flags (PF_R/W/X). + */ + ret = pbl_mmu_setup_from_elf(&elf, membase, memsize); + if (ret) + panic("Failed to setup MMU from ELF: %d\n", ret); + barebox = (void *)(unsigned long)elf.entry; handoff_data_move(handoff_data); diff --git a/include/pbl/mmu.h b/include/pbl/mmu.h new file mode 100644 index 0000000000..72537604e2 --- /dev/null +++ b/include/pbl/mmu.h @@ -0,0 +1,38 @@ +/* SPDX-License-Identifier: GPL-2.0-only */ +#ifndef __PBL_MMU_H +#define __PBL_MMU_H + +#include <linux/types.h> + +struct elf_image; + +/** + * pbl_mmu_setup_from_elf() - Configure MMU using ELF segment information + * @elf: ELF image structure from elf_open_binary_into() + * @membase: Base address of RAM + * @memsize: Size of RAM + * + * This function sets up the MMU with proper permissions based on ELF + * segment flags. It should be called after elf_load_inplace() has + * relocated the barebox image. + * + * Segment permissions are mapped as follows: + * PF_R | PF_X -> Read-only + executable (text) + * PF_R | PF_W -> Read-write (data, bss) + * PF_R -> Read-only (rodata) + * + * Return: 0 on success, negative error code on failure + */ +#if IS_ENABLED(CONFIG_MMU) +int pbl_mmu_setup_from_elf(struct elf_image *elf, unsigned long membase, + unsigned long memsize); +#else +static inline int pbl_mmu_setup_from_elf(struct elf_image *elf, + unsigned long membase, + unsigned long memsize) +{ + return 0; +} +#endif + +#endif /* __PBL_MMU_H */ diff --git a/pbl/Makefile b/pbl/Makefile index f66391be7b..b78124cdcd 100644 --- a/pbl/Makefile +++ b/pbl/Makefile @@ -9,3 +9,4 @@ pbl-$(CONFIG_HAVE_IMAGE_COMPRESSION) += decomp.o pbl-$(CONFIG_LIBFDT) += fdt.o pbl-$(CONFIG_PBL_CONSOLE) += console.o obj-pbl-y += handoff-data.o +obj-pbl-$(CONFIG_MMU) += mmu.o diff --git a/pbl/mmu.c b/pbl/mmu.c new file mode 100644 index 0000000000..744a76afa6 --- /dev/null +++ b/pbl/mmu.c @@ -0,0 +1,105 @@ +// SPDX-License-Identifier: GPL-2.0-only +// SPDX-FileCopyrightText: 2025 Sascha Hauer <[email protected]>, Pengutronix + +#define pr_fmt(fmt) "pbl-mmu: " fmt + +#include <common.h> +#include <elf.h> +#include <mmu.h> +#include <pbl/mmu.h> +#include <asm/mmu.h> +#include <linux/bits.h> +#include <linux/sizes.h> + +/* + * Map ELF segment permissions (p_flags) to architecture MMU flags + */ +static unsigned int elf_flags_to_mmu_flags(u32 p_flags) +{ + bool readable = p_flags & PF_R; + bool writable = p_flags & PF_W; + bool executable = p_flags & PF_X; + + if (readable && writable) { + /* Data, BSS: Read-write, cached, non-executable */ + return MAP_CACHED; + } else if (readable && executable) { + /* Text: Read-only, cached, executable */ + return MAP_CODE; + } else if (readable) { + /* Read-only data: Read-only, cached, non-executable */ + return MAP_CACHED_RO; + } else { + /* + * Unusual: segment with no read permission. + * Map as uncached, non-executable for safety. + */ + pr_warn("Segment with unusual permissions: flags=0x%x\n", p_flags); + return MAP_UNCACHED; + } +} + +int pbl_mmu_setup_from_elf(struct elf_image *elf, unsigned long membase, + unsigned long memsize) +{ + void *phdr; + int i = -1; + + pr_debug("Setting up MMU from ELF segments\n"); + pr_debug("ELF loaded at: 0x%p - 0x%p\n", elf->low_addr, elf->high_addr); + + /* + * Iterate through all PT_LOAD segments and set up MMU permissions + * based on the segment's p_flags + */ + elf_for_each_segment(phdr, elf, elf->hdr_buf) { + i++; + + if (elf_phdr_p_type(elf, phdr) != PT_LOAD) + continue; + + u64 p_vaddr = elf_phdr_p_vaddr(elf, phdr); + u64 p_memsz = elf_phdr_p_memsz(elf, phdr); + u32 p_flags = elf_phdr_p_flags(elf, phdr); + + /* + * Calculate actual address after relocation. + * For ET_EXEC: reloc_offset is 0, use p_vaddr directly + * For ET_DYN: reloc_offset adjusts virtual to actual address + */ + unsigned long addr = p_vaddr + elf->reloc_offset; + unsigned long size = p_memsz; + unsigned long segment_end = addr + size; + + /* Validate segment is within available memory */ + if (segment_end < addr || /* overflow check */ + addr < membase || + segment_end > membase + memsize) { + pr_err("Segment %d outside memory bounds\n", i); + return -EINVAL; + } + + /* Validate alignment - warn and round if needed */ + if (!IS_ALIGNED(size, PAGE_SIZE)) { + pr_debug("Segment %d not page-aligned, rounding\n", i); + size = ALIGN(size, PAGE_SIZE); + } + + unsigned int mmu_flags = elf_flags_to_mmu_flags(p_flags); + + pr_debug("Segment %d: addr=0x%08lx size=0x%08lx flags=0x%x [%c%c%c] -> mmu_flags=0x%x\n", + i, addr, size, p_flags, + (p_flags & PF_R) ? 'R' : '-', + (p_flags & PF_W) ? 'W' : '-', + (p_flags & PF_X) ? 'X' : '-', + mmu_flags); + + /* + * Remap this segment with proper permissions. + */ + remap_range((void *)addr, size, mmu_flags); + } + + pr_debug("MMU setup from ELF complete\n"); + return 0; +} -- 2.47.3
