From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ard Biesheuvel Subject: [PATCH] efi/libstub: arm/arm64: don't use TASK_SIZE when randomising the RT space Date: Mon, 10 Apr 2017 11:30:38 +0100 Message-ID: <20170410103038.20117-1-ard.biesheuvel@linaro.org> Return-path: Sender: linux-efi-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: linux-efi-u79uwXL29TY76Z2rM5mHXA@public.gmane.org Cc: linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org, Ard Biesheuvel , James Morse , Mark Rutland , Catalin Marinas , Matt Fleming , Ingo Molnar List-Id: linux-efi@vger.kernel.org As reported by James, Catalin and Mark, commit e69176d68d26 ("ef/libstub/arm/arm64: Randomize the base of the UEFI rt services region") results in a crash in the firmware regardless of whether KASLR is in effect or not, and whether the firmware implements EFI_RNG_PROTOCOL or not. Mark has identified the root cause to be the inappropriate use of TASK_SIZE in the stub, which arm64 defines as #define TASK_SIZE (test_thread_flag(TIF_32BIT) ? \ TASK_SIZE_32 : TASK_SIZE_64) and testing thread flags at this point results in the dereference of pointers in uninitialized structures. So instead, introduce a preprocessor symbol EFI_RT_VIRTUAL_LIMIT and define it to TASK_SIZE_64 on arm64 and TASK_SIZE on ARM, both of which are compile time constants. Also, change the 'headroom' variable to static const to force an error if this changes in the future. Cc: James Morse Cc: Mark Rutland Cc: Catalin Marinas Cc: Matt Fleming Cc: Ingo Molnar Signed-off-by: Ard Biesheuvel --- Apologies for the breakage. On the systems I have tested, sp_el0 apparently pointed somewhere sane when I inadvertently dereferenced it, and the resulting addresses looked sufficiently random to me. Ingo, once we have some confirmation that this makes the problem go away, could you please take this straight into efi/core? Thanks. drivers/firmware/efi/libstub/arm-stub.c | 11 +++++++++-- 1 file changed, 9 insertions(+), 2 deletions(-) diff --git a/drivers/firmware/efi/libstub/arm-stub.c b/drivers/firmware/efi/libstub/arm-stub.c index 1e45ec51b094..34010ff3b77e 100644 --- a/drivers/firmware/efi/libstub/arm-stub.c +++ b/drivers/firmware/efi/libstub/arm-stub.c @@ -32,6 +32,12 @@ #define EFI_RT_VIRTUAL_BASE SZ_512M #define EFI_RT_VIRTUAL_SIZE SZ_512M +#ifdef CONFIG_ARM64 +#define EFI_RT_VIRTUAL_LIMIT TASK_SIZE_64 +#else +#define EFI_RT_VIRTUAL_LIMIT TASK_SIZE +#endif + static u64 virtmap_base = EFI_RT_VIRTUAL_BASE; efi_status_t efi_open_volume(efi_system_table_t *sys_table_arg, @@ -236,8 +242,9 @@ unsigned long efi_entry(void *handle, efi_system_table_t *sys_table, * 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; + static const u64 headroom = EFI_RT_VIRTUAL_LIMIT - + EFI_RT_VIRTUAL_BASE - + EFI_RT_VIRTUAL_SIZE; u32 rnd; status = efi_get_random_bytes(sys_table, sizeof(rnd), -- 2.9.3 From mboxrd@z Thu Jan 1 00:00:00 1970 From: ard.biesheuvel@linaro.org (Ard Biesheuvel) Date: Mon, 10 Apr 2017 11:30:38 +0100 Subject: [PATCH] efi/libstub: arm/arm64: don't use TASK_SIZE when randomising the RT space Message-ID: <20170410103038.20117-1-ard.biesheuvel@linaro.org> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org As reported by James, Catalin and Mark, commit e69176d68d26 ("ef/libstub/arm/arm64: Randomize the base of the UEFI rt services region") results in a crash in the firmware regardless of whether KASLR is in effect or not, and whether the firmware implements EFI_RNG_PROTOCOL or not. Mark has identified the root cause to be the inappropriate use of TASK_SIZE in the stub, which arm64 defines as #define TASK_SIZE (test_thread_flag(TIF_32BIT) ? \ TASK_SIZE_32 : TASK_SIZE_64) and testing thread flags at this point results in the dereference of pointers in uninitialized structures. So instead, introduce a preprocessor symbol EFI_RT_VIRTUAL_LIMIT and define it to TASK_SIZE_64 on arm64 and TASK_SIZE on ARM, both of which are compile time constants. Also, change the 'headroom' variable to static const to force an error if this changes in the future. Cc: James Morse Cc: Mark Rutland Cc: Catalin Marinas Cc: Matt Fleming Cc: Ingo Molnar Signed-off-by: Ard Biesheuvel --- Apologies for the breakage. On the systems I have tested, sp_el0 apparently pointed somewhere sane when I inadvertently dereferenced it, and the resulting addresses looked sufficiently random to me. Ingo, once we have some confirmation that this makes the problem go away, could you please take this straight into efi/core? Thanks. drivers/firmware/efi/libstub/arm-stub.c | 11 +++++++++-- 1 file changed, 9 insertions(+), 2 deletions(-) diff --git a/drivers/firmware/efi/libstub/arm-stub.c b/drivers/firmware/efi/libstub/arm-stub.c index 1e45ec51b094..34010ff3b77e 100644 --- a/drivers/firmware/efi/libstub/arm-stub.c +++ b/drivers/firmware/efi/libstub/arm-stub.c @@ -32,6 +32,12 @@ #define EFI_RT_VIRTUAL_BASE SZ_512M #define EFI_RT_VIRTUAL_SIZE SZ_512M +#ifdef CONFIG_ARM64 +#define EFI_RT_VIRTUAL_LIMIT TASK_SIZE_64 +#else +#define EFI_RT_VIRTUAL_LIMIT TASK_SIZE +#endif + static u64 virtmap_base = EFI_RT_VIRTUAL_BASE; efi_status_t efi_open_volume(efi_system_table_t *sys_table_arg, @@ -236,8 +242,9 @@ unsigned long efi_entry(void *handle, efi_system_table_t *sys_table, * 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; + static const u64 headroom = EFI_RT_VIRTUAL_LIMIT - + EFI_RT_VIRTUAL_BASE - + EFI_RT_VIRTUAL_SIZE; u32 rnd; status = efi_get_random_bytes(sys_table, sizeof(rnd), -- 2.9.3