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Message-ID: <mhng-bde481b8-a88c-4ba4-b410-da80d1947bcf@palmer-ri-x1c9a>
Date: Sat, 29 Apr 2023 12:50:31 -0700 (PDT)
From: Palmer Dabbelt <palmer@...belt.com>
To: alexghiti@...osinc.com
CC: Paul Walmsley <paul.walmsley@...ive.com>, aou@...s.berkeley.edu,
Ard Biesheuvel <ardb@...nel.org>,
linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
linux-efi@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
alexghiti@...osinc.com
Subject: Re: [PATCH v2 3/4] arm64: libstub: Move KASLR handling functions to efi-stub-helper.c
On Tue, 28 Mar 2023 22:29:25 PDT (-0700), alexghiti@...osinc.com wrote:
> This prepares for riscv to use the same functions to handle the pĥysical
> kernel move when KASLR is enabled.
>
> Signed-off-by: Alexandre Ghiti <alexghiti@...osinc.com>
> ---
> drivers/firmware/efi/libstub/arm64-stub.c | 111 +------------
This LGTM, but I'd prefer at least an Ack from either the Arm or EFI
folks. I think that makes it too late for this merge window.
> .../firmware/efi/libstub/efi-stub-helper.c | 151 ++++++++++++++++++
> drivers/firmware/efi/libstub/efistub.h | 8 +
> 3 files changed, 167 insertions(+), 103 deletions(-)
>
> diff --git a/drivers/firmware/efi/libstub/arm64-stub.c b/drivers/firmware/efi/libstub/arm64-stub.c
> index d4a6b12a8741..b9e0d2cf09aa 100644
> --- a/drivers/firmware/efi/libstub/arm64-stub.c
> +++ b/drivers/firmware/efi/libstub/arm64-stub.c
> @@ -14,42 +14,6 @@
>
> #include "efistub.h"
>
> -/*
> - * Distro versions of GRUB may ignore the BSS allocation entirely (i.e., fail
> - * to provide space, and fail to zero it). Check for this condition by double
> - * checking that the first and the last byte of the image are covered by the
> - * same EFI memory map entry.
> - */
> -static bool check_image_region(u64 base, u64 size)
> -{
> - struct efi_boot_memmap *map;
> - efi_status_t status;
> - bool ret = false;
> - int map_offset;
> -
> - status = efi_get_memory_map(&map, false);
> - if (status != EFI_SUCCESS)
> - return false;
> -
> - for (map_offset = 0; map_offset < map->map_size; map_offset += map->desc_size) {
> - efi_memory_desc_t *md = (void *)map->map + map_offset;
> - u64 end = md->phys_addr + md->num_pages * EFI_PAGE_SIZE;
> -
> - /*
> - * Find the region that covers base, and return whether
> - * it covers base+size bytes.
> - */
> - if (base >= md->phys_addr && base < end) {
> - ret = (base + size) <= end;
> - break;
> - }
> - }
> -
> - efi_bs_call(free_pool, map);
> -
> - return ret;
> -}
> -
> efi_status_t handle_kernel_image(unsigned long *image_addr,
> unsigned long *image_size,
> unsigned long *reserve_addr,
> @@ -59,31 +23,6 @@ efi_status_t handle_kernel_image(unsigned long *image_addr,
> {
> efi_status_t status;
> unsigned long kernel_size, kernel_codesize, kernel_memsize;
> - u32 phys_seed = 0;
> - u64 min_kimg_align = efi_get_kimg_min_align();
> -
> - if (IS_ENABLED(CONFIG_RANDOMIZE_BASE)) {
> - efi_guid_t li_fixed_proto = LINUX_EFI_LOADED_IMAGE_FIXED_GUID;
> - void *p;
> -
> - if (efi_nokaslr) {
> - efi_info("KASLR disabled on kernel command line\n");
> - } else if (efi_bs_call(handle_protocol, image_handle,
> - &li_fixed_proto, &p) == EFI_SUCCESS) {
> - efi_info("Image placement fixed by loader\n");
> - } else {
> - status = efi_get_random_bytes(sizeof(phys_seed),
> - (u8 *)&phys_seed);
> - if (status == EFI_NOT_FOUND) {
> - efi_info("EFI_RNG_PROTOCOL unavailable\n");
> - efi_nokaslr = true;
> - } else if (status != EFI_SUCCESS) {
> - efi_err("efi_get_random_bytes() failed (0x%lx)\n",
> - status);
> - efi_nokaslr = true;
> - }
> - }
> - }
>
> if (image->image_base != _text)
> efi_err("FIRMWARE BUG: efi_loaded_image_t::image_base has bogus value\n");
> @@ -96,49 +35,15 @@ efi_status_t handle_kernel_image(unsigned long *image_addr,
> kernel_codesize = __inittext_end - _text;
> kernel_memsize = kernel_size + (_end - _edata);
> *reserve_size = kernel_memsize;
> + *image_addr = (unsigned long)_text;
>
> - if (IS_ENABLED(CONFIG_RANDOMIZE_BASE) && phys_seed != 0) {
> - /*
> - * If KASLR is enabled, and we have some randomness available,
> - * locate the kernel at a randomized offset in physical memory.
> - */
> - status = efi_random_alloc(*reserve_size, min_kimg_align,
> - reserve_addr, phys_seed,
> - EFI_LOADER_CODE);
> - if (status != EFI_SUCCESS)
> - efi_warn("efi_random_alloc() failed: 0x%lx\n", status);
> - } else {
> - status = EFI_OUT_OF_RESOURCES;
> - }
> -
> - if (status != EFI_SUCCESS) {
> - if (!check_image_region((u64)_text, kernel_memsize)) {
> - efi_err("FIRMWARE BUG: Image BSS overlaps adjacent EFI memory region\n");
> - } else if (IS_ALIGNED((u64)_text, min_kimg_align) &&
> - (u64)_end < EFI_ALLOC_LIMIT) {
> - /*
> - * Just execute from wherever we were loaded by the
> - * UEFI PE/COFF loader if the placement is suitable.
> - */
> - *image_addr = (u64)_text;
> - *reserve_size = 0;
> - return EFI_SUCCESS;
> - }
> -
> - status = efi_allocate_pages_aligned(*reserve_size, reserve_addr,
> - ULONG_MAX, min_kimg_align,
> - EFI_LOADER_CODE);
> -
> - if (status != EFI_SUCCESS) {
> - efi_err("Failed to relocate kernel\n");
> - *reserve_size = 0;
> - return status;
> - }
> - }
> -
> - *image_addr = *reserve_addr;
> - memcpy((void *)*image_addr, _text, kernel_size);
> - caches_clean_inval_pou(*image_addr, *image_addr + kernel_codesize);
> + status = efi_kaslr_relocate_kernel(image_addr,
> + reserve_addr, reserve_size,
> + kernel_size, kernel_codesize,
> + kernel_memsize,
> + efi_kaslr_get_phys_seed(image_handle));
> + if (status != EFI_SUCCESS)
> + return status;
>
> return EFI_SUCCESS;
> }
> diff --git a/drivers/firmware/efi/libstub/efi-stub-helper.c b/drivers/firmware/efi/libstub/efi-stub-helper.c
> index 1e0203d74691..40ac2625949c 100644
> --- a/drivers/firmware/efi/libstub/efi-stub-helper.c
> +++ b/drivers/firmware/efi/libstub/efi-stub-helper.c
> @@ -718,3 +718,154 @@ void efi_remap_image(unsigned long image_base, unsigned alloc_size,
> efi_warn("Failed to remap data region non-executable\n");
> }
> }
> +
> +/**
> + * efi_kaslr_get_phys_seed() - Get random seed for physical kernel KASLR
> + * @image_handle: Handle to the image
> + *
> + * If KASLR is not disabled, obtain a random seed using EFI_RNG_PROTOCOL
> + * that will be used to move the kernel physical mapping.
> + *
> + * Return: the random seed
> + */
> +u32 efi_kaslr_get_phys_seed(efi_handle_t image_handle)
> +{
> + efi_status_t status;
> + u32 phys_seed;
> + efi_guid_t li_fixed_proto = LINUX_EFI_LOADED_IMAGE_FIXED_GUID;
> + void *p;
> +
> + if (!IS_ENABLED(CONFIG_RANDOMIZE_BASE))
> + return 0;
> +
> + if (efi_nokaslr) {
> + efi_info("KASLR disabled on kernel command line\n");
> + } else if (efi_bs_call(handle_protocol, image_handle,
> + &li_fixed_proto, &p) == EFI_SUCCESS) {
> + efi_info("Image placement fixed by loader\n");
> + } else {
> + status = efi_get_random_bytes(sizeof(phys_seed),
> + (u8 *)&phys_seed);
> + if (status == EFI_SUCCESS) {
> + return phys_seed;
> + } else if (status == EFI_NOT_FOUND) {
> + efi_info("EFI_RNG_PROTOCOL unavailable\n");
> + efi_nokaslr = true;
> + } else if (status != EFI_SUCCESS) {
> + efi_err("efi_get_random_bytes() failed (0x%lx)\n",
> + status);
> + efi_nokaslr = true;
> + }
> + }
> +
> + return 0;
> +}
> +
> +/*
> + * Distro versions of GRUB may ignore the BSS allocation entirely (i.e., fail
> + * to provide space, and fail to zero it). Check for this condition by double
> + * checking that the first and the last byte of the image are covered by the
> + * same EFI memory map entry.
> + */
> +static bool check_image_region(u64 base, u64 size)
> +{
> + struct efi_boot_memmap *map;
> + efi_status_t status;
> + bool ret = false;
> + int map_offset;
> +
> + status = efi_get_memory_map(&map, false);
> + if (status != EFI_SUCCESS)
> + return false;
> +
> + for (map_offset = 0; map_offset < map->map_size; map_offset += map->desc_size) {
> + efi_memory_desc_t *md = (void *)map->map + map_offset;
> + u64 end = md->phys_addr + md->num_pages * EFI_PAGE_SIZE;
> +
> + /*
> + * Find the region that covers base, and return whether
> + * it covers base+size bytes.
> + */
> + if (base >= md->phys_addr && base < end) {
> + ret = (base + size) <= end;
> + break;
> + }
> + }
> +
> + efi_bs_call(free_pool, map);
> +
> + return ret;
> +}
> +
> +/**
> + * efi_kaslr_relocate_kernel() - Relocate the kernel (random if KASLR enabled)
> + * @image_addr: Pointer to the current kernel location
> + * @reserve_addr: Pointer to the relocated kernel location
> + * @reserve_size: Size of the relocated kernel
> + * @kernel_size: Size of the text + data
> + * @kernel_codesize: Size of the text
> + * @kernel_memsize: Size of the text + data + bss
> + * @phys_seed: Random seed used for the relocation
> + *
> + * If KASLR is not enabled, this function relocates the kernel to a fixed
> + * address (or leave it as its current location). If KASLR is enabled, the
> + * kernel physical location is randomized using the seed in parameter.
> + *
> + * Return: status code, EFI_SUCCESS if relocation is successful
> + */
> +efi_status_t efi_kaslr_relocate_kernel(unsigned long *image_addr,
> + unsigned long *reserve_addr,
> + unsigned long *reserve_size,
> + unsigned long kernel_size,
> + unsigned long kernel_codesize,
> + unsigned long kernel_memsize,
> + u32 phys_seed)
> +{
> + efi_status_t status;
> + u64 min_kimg_align = efi_get_kimg_min_align();
> +
> + if (IS_ENABLED(CONFIG_RANDOMIZE_BASE) && phys_seed != 0) {
> + /*
> + * If KASLR is enabled, and we have some randomness available,
> + * locate the kernel at a randomized offset in physical memory.
> + */
> + status = efi_random_alloc(*reserve_size, min_kimg_align,
> + reserve_addr, phys_seed,
> + EFI_LOADER_CODE);
> + if (status != EFI_SUCCESS)
> + efi_warn("efi_random_alloc() failed: 0x%lx\n", status);
> + } else {
> + status = EFI_OUT_OF_RESOURCES;
> + }
> +
> + if (status != EFI_SUCCESS) {
> + if (!check_image_region(*image_addr, kernel_memsize)) {
> + efi_err("FIRMWARE BUG: Image BSS overlaps adjacent EFI memory region\n");
> + } else if (IS_ALIGNED(*image_addr, min_kimg_align) &&
> + (u64)_end < EFI_ALLOC_LIMIT) {
> + /*
> + * Just execute from wherever we were loaded by the
> + * UEFI PE/COFF loader if the placement is suitable.
> + */
> + *reserve_size = 0;
> + return EFI_SUCCESS;
> + }
> +
> + status = efi_allocate_pages_aligned(*reserve_size, reserve_addr,
> + ULONG_MAX, min_kimg_align,
> + EFI_LOADER_CODE);
> +
> + if (status != EFI_SUCCESS) {
> + efi_err("Failed to relocate kernel\n");
> + *reserve_size = 0;
> + return status;
> + }
> + }
> +
> + memcpy((void *)*reserve_addr, (void *)*image_addr, kernel_size);
> + *image_addr = *reserve_addr;
> +
> + caches_clean_inval_pou(*image_addr, *image_addr + kernel_codesize);
> +
> + return status;
> +}
> diff --git a/drivers/firmware/efi/libstub/efistub.h b/drivers/firmware/efi/libstub/efistub.h
> index 6bd3bb86d967..64273371ce96 100644
> --- a/drivers/firmware/efi/libstub/efistub.h
> +++ b/drivers/firmware/efi/libstub/efistub.h
> @@ -1098,5 +1098,13 @@ const u8 *__efi_get_smbios_string(u8 type, int offset, int recsize);
>
> void efi_remap_image(unsigned long image_base, unsigned alloc_size,
> unsigned long code_size);
> +efi_status_t efi_kaslr_relocate_kernel(unsigned long *image_addr,
> + unsigned long *reserve_addr,
> + unsigned long *reserve_size,
> + unsigned long kernel_size,
> + unsigned long kernel_codesize,
> + unsigned long kernel_memsize,
> + u32 phys_seed);
> +u32 efi_kaslr_get_phys_seed(efi_handle_t image_handle);
>
> #endif
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