Hi,
On 1/5/26 12:26 PM, Sascha Hauer wrote:
> /*
> - * Early mmu init will have mapped everything but the initial memory
> area
> - * (excluding final OPTEE_SIZE bytes) uncached. We have now discovered
> - * all memory banks, so let's map all pages, excluding reserved memory
> areas
> - * and barebox text area cacheable.
> - *
> - * This code will become much less complex once we switch over to using
> - * CONFIG_MEMORY_ATTRIBUTES for MMU as well.
> + * PBL has already set up the MMU with proper permissions based on
> + * ELF segment information. We only need to set up trap pages for
> + * exception handling.
This is incorrect. PBL only know about initial memory and not about
other memory banks and reserved memory regions. We need to keep this code...
> */
> - for_each_memory_bank(bank) {
> - struct resource *rsv;
> - resource_size_t pos;
> -
> - pos = bank->start;
> -
> - /* Skip reserved regions */
> - for_each_reserved_region(bank, rsv) {
> - if (pos != rsv->start)
> - remap_range_end_sans_text(pos, rsv->start,
> MAP_CACHED);
> - pos = rsv->end + 1;
> - }
> -
> - remap_range_end_sans_text(pos, bank->start + bank->size,
> MAP_CACHED);
> - }
> -
> - /* Do this while interrupt vectors are still writable */
> setup_trap_pages();
> -
> - remap_range((void *)code_start, code_size, MAP_CODE);
> - remap_range((void *)rodata_start, rodata_size, MAP_CACHED_RO);
These two lines however are fine to remove now.
> + /*
> + * 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).
> + */
> + if (IS_ENABLED(CONFIG_MMU)) {
> + ret = pbl_mmu_setup_from_elf(&elf, membase, memsize);
I think it might be cleaner to move the ELF logic to pbl/elf.c given
that it's common for both ARM and RISC-V?
> +/**
> + * 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
> + */
> +int pbl_mmu_setup_from_elf(struct elf_image *elf, unsigned long membase,
> + unsigned long memsize);
> +
> +#endif /* __PBL_MMU_H */
> diff --git a/pbl/Makefile b/pbl/Makefile
> index
> f66391be7b2898388425657f54afcd6e4c72e3db..b78124cdcd2a4690be11d5503006723252b4904f
> 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
> 0000000000000000000000000000000000000000..7a8f254a7bd67eccaab715832930c5d4134eb288
> --- /dev/null
> +++ b/pbl/mmu.c
> @@ -0,0 +1,111 @@
> +// 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;
Nitpick: A switch (p_flags & (PF_R | PF_W | PF_X)) might look neater.
> + } 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;
> + int phnum = elf_hdr_e_phnum(elf, elf->hdr_buf);
> + size_t phoff = elf_hdr_e_phoff(elf, elf->hdr_buf);
> + size_t phentsize = elf_size_of_phdr(elf);
> +
> + pr_debug("Setting up MMU from ELF segments\n");
> + pr_debug("ELF entry point: 0x%llx\n", elf->entry);
> + 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
> + */
> + for (i = 0; i < phnum; i++) {
> + phdr = elf->hdr_buf + phoff + i * phentsize;
> +
> + 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;
Add a check to skip non-alloc segments? We could use that to include
info that's only used in PBL and discarded after (e.g. dynsym table).
> +
> + /* 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(addr, SZ_4K) || !IS_ALIGNED(size, SZ_4K)) {
s/SZ_4K/PAGE_SIZE/
> + pr_warn("Segment %d not page-aligned, rounding\n", i);
> + size = ALIGN(size, SZ_4K);
Don't you get a warning every time for PT_DYNAMIC this way?
Cheers,
Ahmad
> + }
> +
> + 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.
> + * Use page-wise mapping to allow different permissions for
> + * different segments even if they're nearby.
> + */
> + pbl_remap_range((void *)addr, addr, size, mmu_flags);
> + }
> +
> + pr_debug("MMU setup from ELF complete\n");
> + return 0;
> +}
>
--
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