From e69176d68d26d63d9214797c191ce65358ea1ecf Mon Sep 17 00:00:00 2001 From: Ard Biesheuvel Date: Tue, 4 Apr 2017 17:09:10 +0100 Subject: [PATCH] ef/libstub/arm/arm64: Randomize the base of the UEFI rt services region Update the allocation logic for the virtual mapping of the UEFI runtime services to start from a randomized base address if KASLR is in effect, and if the UEFI firmware exposes an implementation of EFI_RNG_PROTOCOL. This makes it more difficult to predict the location of exploitable data structures in the runtime UEFI firmware, which increases robustness against attacks. Note that these regions are only mapped during the time a runtime service call is in progress, and only on a single CPU at a time, bit given the lack of a downside, let's enable it nonetheless. Signed-off-by: Ard Biesheuvel Cc: Borislav Petkov Cc: Linus Torvalds Cc: Matt Fleming Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: bhe@redhat.com Cc: bhsharma@redhat.com Cc: eugene@hp.com Cc: evgeny.kalugin@intel.com Cc: jhugo@codeaurora.org Cc: leif.lindholm@linaro.org Cc: linux-efi@vger.kernel.org Cc: mark.rutland@arm.com Cc: roy.franz@cavium.com Cc: rruigrok@codeaurora.org Link: http://lkml.kernel.org/r/20170404160910.28115-3-ard.biesheuvel@linaro.org Signed-off-by: Ingo Molnar --- drivers/firmware/efi/libstub/arm-stub.c | 49 ++++++++++++++++++------- 1 file changed, 36 insertions(+), 13 deletions(-) diff --git a/drivers/firmware/efi/libstub/arm-stub.c b/drivers/firmware/efi/libstub/arm-stub.c index 657bb72c9e0b..1e45ec51b094 100644 --- a/drivers/firmware/efi/libstub/arm-stub.c +++ b/drivers/firmware/efi/libstub/arm-stub.c @@ -18,6 +18,22 @@ #include "efistub.h" +/* + * This is the base address at which to start allocating virtual memory ranges + * for UEFI Runtime Services. This is in the low TTBR0 range so that we can use + * any allocation we choose, and eliminate the risk of a conflict after kexec. + * The value chosen is the largest non-zero power of 2 suitable for this purpose + * both on 32-bit and 64-bit ARM CPUs, to maximize the likelihood that it can + * be mapped efficiently. + * Since 32-bit ARM could potentially execute with a 1G/3G user/kernel split, + * map everything below 1 GB. (512 MB is a reasonable upper bound for the + * entire footprint of the UEFI runtime services memory regions) + */ +#define EFI_RT_VIRTUAL_BASE SZ_512M +#define EFI_RT_VIRTUAL_SIZE SZ_512M + +static u64 virtmap_base = EFI_RT_VIRTUAL_BASE; + efi_status_t efi_open_volume(efi_system_table_t *sys_table_arg, void *__image, void **__fh) { @@ -213,6 +229,25 @@ unsigned long efi_entry(void *handle, efi_system_table_t *sys_table, efi_random_get_seed(sys_table); + if (!nokaslr()) { + /* + * Randomize the base of the UEFI runtime services region. + * Preserve the 2 MB alignment of the region by taking a + * shift of 21 bit positions into account when scaling + * the headroom value using a 32-bit random value. + */ + u64 headroom = TASK_SIZE - EFI_RT_VIRTUAL_BASE - + EFI_RT_VIRTUAL_SIZE; + u32 rnd; + + status = efi_get_random_bytes(sys_table, sizeof(rnd), + (u8 *)&rnd); + if (status == EFI_SUCCESS) { + virtmap_base = EFI_RT_VIRTUAL_BASE + + (((headroom >> 21) * rnd) >> (32 - 21)); + } + } + new_fdt_addr = fdt_addr; status = allocate_new_fdt_and_exit_boot(sys_table, handle, &new_fdt_addr, efi_get_max_fdt_addr(dram_base), @@ -242,18 +277,6 @@ fail: return EFI_ERROR; } -/* - * This is the base address at which to start allocating virtual memory ranges - * for UEFI Runtime Services. This is in the low TTBR0 range so that we can use - * any allocation we choose, and eliminate the risk of a conflict after kexec. - * The value chosen is the largest non-zero power of 2 suitable for this purpose - * both on 32-bit and 64-bit ARM CPUs, to maximize the likelihood that it can - * be mapped efficiently. - * Since 32-bit ARM could potentially execute with a 1G/3G user/kernel split, - * map everything below 1 GB. - */ -#define EFI_RT_VIRTUAL_BASE SZ_512M - static int cmp_mem_desc(const void *l, const void *r) { const efi_memory_desc_t *left = l, *right = r; @@ -303,7 +326,7 @@ void efi_get_virtmap(efi_memory_desc_t *memory_map, unsigned long map_size, unsigned long desc_size, efi_memory_desc_t *runtime_map, int *count) { - u64 efi_virt_base = EFI_RT_VIRTUAL_BASE; + u64 efi_virt_base = virtmap_base; efi_memory_desc_t *in, *prev = NULL, *out = runtime_map; int l; -- 2.20.1