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 <[email protected]>
Cc: Diana Craciun <[email protected]>
Cc: Michael Ellerman <[email protected]>
Cc: Christophe Leroy <[email protected]>
Cc: Benjamin Herrenschmidt <[email protected]>
Cc: Paul Mackerras <[email protected]>
Cc: Nicholas Piggin <[email protected]>
Cc: Kees Cook <[email protected]>
---
arch/powerpc/kernel/kaslr_booke.c | 334 +++++++++++++++++++++++++++++-
1 file changed, 332 insertions(+), 2 deletions(-)
diff --git a/arch/powerpc/kernel/kaslr_booke.c b/arch/powerpc/kernel/kaslr_booke.c
index 960bce4aa8b9..0bb02e45b928 100644
--- a/arch/powerpc/kernel/kaslr_booke.c
+++ b/arch/powerpc/kernel/kaslr_booke.c
@@ -23,6 +23,8 @@
#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>
@@ -34,15 +36,341 @@
#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 __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(boot_command_line, cmdline, COMMAND_LINE_SIZE);
+}
+
+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_CRASH_CORE
+ unsigned long long crash_size, crash_base;
+ int ret;
+
+ ret = parse_crashkernel(boot_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;
}
/*
@@ -59,6 +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)
--
2.17.2
Le 30/07/2019 à 09:42, 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 <[email protected]>
> Cc: Diana Craciun <[email protected]>
> Cc: Michael Ellerman <[email protected]>
> Cc: Christophe Leroy <[email protected]>
> Cc: Benjamin Herrenschmidt <[email protected]>
> Cc: Paul Mackerras <[email protected]>
> Cc: Nicholas Piggin <[email protected]>
> Cc: Kees Cook <[email protected]>
> ---
> arch/powerpc/kernel/kaslr_booke.c | 334 +++++++++++++++++++++++++++++-
> 1 file changed, 332 insertions(+), 2 deletions(-)
>
> diff --git a/arch/powerpc/kernel/kaslr_booke.c b/arch/powerpc/kernel/kaslr_booke.c
> index 960bce4aa8b9..0bb02e45b928 100644
> --- a/arch/powerpc/kernel/kaslr_booke.c
> +++ b/arch/powerpc/kernel/kaslr_booke.c
> @@ -23,6 +23,8 @@
> #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>
> @@ -34,15 +36,341 @@
> #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 __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(boot_command_line, cmdline, COMMAND_LINE_SIZE);
boot_command_line is set by early_init_devtree() in
arch/powerpc/kernel/prom.c
Is that too late for you ?
If so, what about calling early_init_dt_scan_chosen() instead of recoding ?
Christophe
On 2019/7/30 17:44, Christophe Leroy wrote:
>
>
> Le 30/07/2019 à 09:42, 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 <[email protected]>
>> Cc: Diana Craciun <[email protected]>
>> Cc: Michael Ellerman <[email protected]>
>> Cc: Christophe Leroy <[email protected]>
>> Cc: Benjamin Herrenschmidt <[email protected]>
>> Cc: Paul Mackerras <[email protected]>
>> Cc: Nicholas Piggin <[email protected]>
>> Cc: Kees Cook <[email protected]>
>> ---
>> arch/powerpc/kernel/kaslr_booke.c | 334 +++++++++++++++++++++++++++++-
>> 1 file changed, 332 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/powerpc/kernel/kaslr_booke.c
>> b/arch/powerpc/kernel/kaslr_booke.c
>> index 960bce4aa8b9..0bb02e45b928 100644
>> --- a/arch/powerpc/kernel/kaslr_booke.c
>> +++ b/arch/powerpc/kernel/kaslr_booke.c
>> @@ -23,6 +23,8 @@
>> #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>
>> @@ -34,15 +36,341 @@
>> #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 __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(boot_command_line, cmdline, COMMAND_LINE_SIZE);
>
> boot_command_line is set by early_init_devtree() in
> arch/powerpc/kernel/prom.c
> Is that too late for you ?
>
Yes, it's too late.
> If so, what about calling early_init_dt_scan_chosen() instead of recoding ?
>
Good suggestion. I will have a try.
> Christophe
>
> .
>