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Message-ID: <d2ed1821-96a2-d7eb-4c1e-4787c7dd467a@c-s.fr>
Date: Mon, 29 Jul 2019 13:33:29 +0200
From: Christophe Leroy <christophe.leroy@....fr>
To: Jason Yan <yanaijie@...wei.com>, mpe@...erman.id.au,
linuxppc-dev@...ts.ozlabs.org, diana.craciun@....com,
benh@...nel.crashing.org, paulus@...ba.org, npiggin@...il.com,
keescook@...omium.org, kernel-hardening@...ts.openwall.com
Cc: linux-kernel@...r.kernel.org, wangkefeng.wang@...wei.com,
yebin10@...wei.com, thunder.leizhen@...wei.com, jingxiangfeng@...wei.com,
fanchengyang@...wei.com
Subject: Re: [RFC PATCH 07/10] powerpc/fsl_booke/32: randomize the kernel
image offset
Le 17/07/2019 à 10:06, Jason Yan a écrit :
> After we have the basic support of relocate the kernel in some
> appropriate place, we can start to randomize the offset now.
>
> Entropy is derived from the banner and timer, which will change every
> build and boot. This not so much safe so additionally the bootloader may
> pass entropy via the /chosen/kaslr-seed node in device tree.
>
> We will use the first 512M of the low memory to randomize the kernel
> image. The memory will be split in 64M zones. We will use the lower 8
> bit of the entropy to decide the index of the 64M zone. Then we chose a
> 16K aligned offset inside the 64M zone to put the kernel in.
>
> KERNELBASE
>
> |--> 64M <--|
> | |
> +---------------+ +----------------+---------------+
> | |....| |kernel| | |
> +---------------+ +----------------+---------------+
> | |
> |-----> offset <-----|
>
> kimage_vaddr
>
> We also check if we will overlap with some areas like the dtb area, the
> initrd area or the crashkernel area. If we cannot find a proper area,
> kaslr will be disabled and boot from the original kernel.
>
> Signed-off-by: Jason Yan <yanaijie@...wei.com>
> Cc: Diana Craciun <diana.craciun@....com>
> Cc: Michael Ellerman <mpe@...erman.id.au>
> Cc: Christophe Leroy <christophe.leroy@....fr>
> Cc: Benjamin Herrenschmidt <benh@...nel.crashing.org>
> Cc: Paul Mackerras <paulus@...ba.org>
> Cc: Nicholas Piggin <npiggin@...il.com>
> Cc: Kees Cook <keescook@...omium.org>
> ---
> arch/powerpc/kernel/kaslr_booke.c | 335 +++++++++++++++++++++++++++++-
> 1 file changed, 333 insertions(+), 2 deletions(-)
>
> diff --git a/arch/powerpc/kernel/kaslr_booke.c b/arch/powerpc/kernel/kaslr_booke.c
> index 72d8e9432048..90357f4bd313 100644
> --- a/arch/powerpc/kernel/kaslr_booke.c
> +++ b/arch/powerpc/kernel/kaslr_booke.c
> @@ -22,6 +22,8 @@
> #include <linux/delay.h>
> #include <linux/highmem.h>
> #include <linux/memblock.h>
> +#include <linux/libfdt.h>
> +#include <linux/crash_core.h>
> #include <asm/pgalloc.h>
> #include <asm/prom.h>
> #include <asm/io.h>
> @@ -33,15 +35,342 @@
> #include <asm/machdep.h>
> #include <asm/setup.h>
> #include <asm/paca.h>
> +#include <asm/kdump.h>
> #include <mm/mmu_decl.h>
> +#include <generated/compile.h>
> +#include <generated/utsrelease.h>
> +
> +#ifdef DEBUG
> +#define DBG(fmt...) printk(KERN_ERR fmt)
> +#else
> +#define DBG(fmt...)
> +#endif
> +
> +struct regions {
> + unsigned long pa_start;
> + unsigned long pa_end;
> + unsigned long kernel_size;
> + unsigned long dtb_start;
> + unsigned long dtb_end;
> + unsigned long initrd_start;
> + unsigned long initrd_end;
> + unsigned long crash_start;
> + unsigned long crash_end;
> + int reserved_mem;
> + int reserved_mem_addr_cells;
> + int reserved_mem_size_cells;
> +};
>
> extern int is_second_reloc;
>
> +/* Simplified build-specific string for starting entropy. */
> +static const char build_str[] = UTS_RELEASE " (" LINUX_COMPILE_BY "@"
> + LINUX_COMPILE_HOST ") (" LINUX_COMPILER ") " UTS_VERSION;
> +static char __initdata early_command_line[COMMAND_LINE_SIZE];
> +
> +static __init void kaslr_get_cmdline(void *fdt)
> +{
> + const char *cmdline = CONFIG_CMDLINE;
> + if (!IS_ENABLED(CONFIG_CMDLINE_FORCE)) {
> + int node;
> + const u8 *prop;
> + node = fdt_path_offset(fdt, "/chosen");
> + if (node < 0)
> + goto out;
> +
> + prop = fdt_getprop(fdt, node, "bootargs", NULL);
> + if (!prop)
> + goto out;
> + cmdline = prop;
> + }
> +out:
> + strscpy(early_command_line, cmdline, COMMAND_LINE_SIZE);
> +}
> +
Can you explain why we need that and can't use the already existing
cmdline stuff ?
Christophe
> +static unsigned long __init rotate_xor(unsigned long hash, const void *area,
> + size_t size)
> +{
> + size_t i;
> + unsigned long *ptr = (unsigned long *)area;
> +
> + for (i = 0; i < size / sizeof(hash); i++) {
> + /* Rotate by odd number of bits and XOR. */
> + hash = (hash << ((sizeof(hash) * 8) - 7)) | (hash >> 7);
> + hash ^= ptr[i];
> + }
> +
> + return hash;
> +}
> +
> +/* Attempt to create a simple but unpredictable starting entropy. */
> +static unsigned long __init get_boot_seed(void *fdt)
> +{
> + unsigned long hash = 0;
> +
> + hash = rotate_xor(hash, build_str, sizeof(build_str));
> + hash = rotate_xor(hash, fdt, fdt_totalsize(fdt));
> +
> + return hash;
> +}
> +
> +static __init u64 get_kaslr_seed(void *fdt)
> +{
> + int node, len;
> + fdt64_t *prop;
> + u64 ret;
> +
> + node = fdt_path_offset(fdt, "/chosen");
> + if (node < 0)
> + return 0;
> +
> + prop = fdt_getprop_w(fdt, node, "kaslr-seed", &len);
> + if (!prop || len != sizeof(u64))
> + return 0;
> +
> + ret = fdt64_to_cpu(*prop);
> + *prop = 0;
> + return ret;
> +}
> +
> +static __init bool regions_overlap(u32 s1, u32 e1, u32 s2, u32 e2)
> +{
> + return e1 >= s2 && e2 >= s1;
> +}
> +
> +static __init bool overlaps_reserved_region(const void *fdt, u32 start,
> + u32 end, struct regions *regions)
> +{
> + int subnode, len, i;
> + u64 base, size;
> +
> + /* check for overlap with /memreserve/ entries */
> + for (i = 0; i < fdt_num_mem_rsv(fdt); i++) {
> + if (fdt_get_mem_rsv(fdt, i, &base, &size) < 0)
> + continue;
> + if (regions_overlap(start, end, base, base + size))
> + return true;
> + }
> +
> + if (regions->reserved_mem < 0)
> + return false;
> +
> + /* check for overlap with static reservations in /reserved-memory */
> + for (subnode = fdt_first_subnode(fdt, regions->reserved_mem);
> + subnode >= 0;
> + subnode = fdt_next_subnode(fdt, subnode)) {
> + const fdt32_t *reg;
> + u64 rsv_end;
> +
> + len = 0;
> + reg = fdt_getprop(fdt, subnode, "reg", &len);
> + while (len >= (regions->reserved_mem_addr_cells +
> + regions->reserved_mem_size_cells)) {
> + base = fdt32_to_cpu(reg[0]);
> + if (regions->reserved_mem_addr_cells == 2)
> + base = (base << 32) | fdt32_to_cpu(reg[1]);
> +
> + reg += regions->reserved_mem_addr_cells;
> + len -= 4 * regions->reserved_mem_addr_cells;
> +
> + size = fdt32_to_cpu(reg[0]);
> + if (regions->reserved_mem_size_cells == 2)
> + size = (size << 32) | fdt32_to_cpu(reg[1]);
> +
> + reg += regions->reserved_mem_size_cells;
> + len -= 4 * regions->reserved_mem_size_cells;
> +
> + if (base >= regions->pa_end)
> + continue;
> +
> + rsv_end = min(base + size, (u64)U32_MAX);
> +
> + if (regions_overlap(start, end, base, rsv_end))
> + return true;
> + }
> + }
> + return false;
> +}
> +
> +static __init bool overlaps_region(const void *fdt, u32 start,
> + u32 end, struct regions *regions)
> +{
> + if (regions_overlap(start, end, regions->dtb_start,
> + regions->dtb_end))
> + return true;
> +
> + if (regions_overlap(start, end, regions->initrd_start,
> + regions->initrd_end))
> + return true;
> +
> + if (regions_overlap(start, end, regions->crash_start,
> + regions->crash_end))
> + return true;
> +
> + return overlaps_reserved_region(fdt, start, end, regions);
> +}
> +
> +static void __init get_crash_kernel(void *fdt, unsigned long size,
> + struct regions *regions)
> +{
> +#ifdef CONFIG_KEXEC_CORE
> + unsigned long long crash_size, crash_base;
> + int ret;
> +
> + ret = parse_crashkernel(early_command_line, size, &crash_size,
> + &crash_base);
> + if (ret != 0 || crash_size == 0)
> + return;
> + if (crash_base == 0)
> + crash_base = KDUMP_KERNELBASE;
> +
> + regions->crash_start = (unsigned long)crash_base;
> + regions->crash_end = (unsigned long)(crash_base + crash_size);
> +
> + DBG("crash_base=0x%llx crash_size=0x%llx\n", crash_base, crash_size);
> +#endif
> +}
> +
> +static void __init get_initrd_range(void *fdt, struct regions *regions)
> +{
> + u64 start, end;
> + int node, len;
> + const __be32 *prop;
> +
> + node = fdt_path_offset(fdt, "/chosen");
> + if (node < 0)
> + return;
> +
> + prop = fdt_getprop(fdt, node, "linux,initrd-start", &len);
> + if (!prop)
> + return;
> + start = of_read_number(prop, len / 4);
> +
> + prop = fdt_getprop(fdt, node, "linux,initrd-end", &len);
> + if (!prop)
> + return;
> + end = of_read_number(prop, len / 4);
> +
> + regions->initrd_start = (unsigned long)start;
> + regions->initrd_end = (unsigned long)end;
> +
> + DBG("initrd_start=0x%llx initrd_end=0x%llx\n", start, end);
> +}
> +
> +static __init unsigned long get_usable_offset(const void *fdt, struct regions *regions,
> + unsigned long start)
> +{
> + unsigned long pa;
> + unsigned long pa_end;
> +
> + for (pa = start; pa > regions->pa_start; pa -= SZ_16K) {
> + pa_end = pa + regions->kernel_size;
> + if (overlaps_region(fdt, pa, pa_end, regions))
> + continue;
> +
> + return pa;
> + }
> + return 0;
> +}
> +
> +static __init void get_cell_sizes(const void *fdt, int node, int *addr_cells,
> + int *size_cells)
> +{
> + const int *prop;
> + int len;
> +
> + /*
> + * Retrieve the #address-cells and #size-cells properties
> + * from the 'node', or use the default if not provided.
> + */
> + *addr_cells = *size_cells = 1;
> +
> + prop = fdt_getprop(fdt, node, "#address-cells", &len);
> + if (len == 4)
> + *addr_cells = fdt32_to_cpu(*prop);
> + prop = fdt_getprop(fdt, node, "#size-cells", &len);
> + if (len == 4)
> + *size_cells = fdt32_to_cpu(*prop);
> +}
> +
> static unsigned long __init kaslr_choose_location(void *dt_ptr, phys_addr_t size,
> unsigned long kernel_sz)
> {
> - /* return a fixed offset of 64M for now */
> - return 0x4000000;
> + unsigned long offset, random;
> + unsigned long ram, linear_sz;
> + unsigned long kaslr_offset;
> + u64 seed;
> + struct regions regions;
> + unsigned long index;
> +
> + random = get_boot_seed(dt_ptr);
> +
> + seed = get_tb() << 32;
> + seed ^= get_tb();
> + random = rotate_xor(random, &seed, sizeof(seed));
> +
> + /*
> + * Retrieve (and wipe) the seed from the FDT
> + */
> + seed = get_kaslr_seed(dt_ptr);
> + if (seed)
> + random = rotate_xor(random, &seed, sizeof(seed));
> +
> + ram = min((phys_addr_t)__max_low_memory, size);
> + ram = map_mem_in_cams(ram, CONFIG_LOWMEM_CAM_NUM, true);
> + linear_sz = min(ram, (unsigned long)SZ_512M);
> +
> + /* If the linear size is smaller than 64M, do not randmize */
> + if (linear_sz < SZ_64M)
> + return 0;
> +
> + memset(®ions, 0, sizeof(regions));
> +
> + /* check for a reserved-memory node and record its cell sizes */
> + regions.reserved_mem = fdt_path_offset(dt_ptr, "/reserved-memory");
> + if (regions.reserved_mem >= 0)
> + get_cell_sizes(dt_ptr, regions.reserved_mem,
> + ®ions.reserved_mem_addr_cells,
> + ®ions.reserved_mem_size_cells);
> +
> + regions.pa_start = 0;
> + regions.pa_end = linear_sz;
> + regions.dtb_start = __pa(dt_ptr);
> + regions.dtb_end = __pa(dt_ptr) + fdt_totalsize(dt_ptr);
> + regions.kernel_size = kernel_sz;
> +
> + get_initrd_range(dt_ptr, ®ions);
> + get_crash_kernel(dt_ptr, ram, ®ions);
> +
> + /*
> + * Decide which 64M we want to start
> + * Only use the low 8 bits of the random seed
> + */
> + index = random & 0xFF;
> + index %= linear_sz / SZ_64M;
> +
> + /* Decide offset inside 64M */
> + if (index == 0) {
> + offset = random % (SZ_64M - round_up(kernel_sz, SZ_16K) * 2);
> + offset += round_up(kernel_sz, SZ_16K);
> + offset = round_up(offset, SZ_16K);
> + } else {
> + offset = random % (SZ_64M - kernel_sz);
> + offset = round_down(offset, SZ_16K);
> + }
> +
> + while (index >= 0) {
> + offset = offset + index * SZ_64M;
> + kaslr_offset = get_usable_offset(dt_ptr, ®ions, offset);
> + if (kaslr_offset)
> + break;
> + index--;
> + }
> +
> + /* Did not find any usable region? Give up randomize */
> + if (index < 0)
> + kaslr_offset = 0;
> +
> + return kaslr_offset;
> }
>
> /*
> @@ -58,6 +387,8 @@ notrace void __init kaslr_early_init(void *dt_ptr, phys_addr_t size)
>
> kernel_sz = (unsigned long)_end - KERNELBASE;
>
> + kaslr_get_cmdline(dt_ptr);
> +
> offset = kaslr_choose_location(dt_ptr, size, kernel_sz);
>
> if (offset == 0)
>
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