From 220dd7699c46d5940115bd797b01b2ab047c87b8 Mon Sep 17 00:00:00 2001 From: Kairui Song Date: Tue, 29 Oct 2019 18:37:54 +0100 Subject: x86, efi: Never relocate kernel below lowest acceptable address Currently, kernel fails to boot on some HyperV VMs when using EFI. And it's a potential issue on all x86 platforms. It's caused by broken kernel relocation on EFI systems, when below three conditions are met: 1. Kernel image is not loaded to the default address (LOAD_PHYSICAL_ADDR) by the loader. 2. There isn't enough room to contain the kernel, starting from the default load address (eg. something else occupied part the region). 3. In the memmap provided by EFI firmware, there is a memory region starts below LOAD_PHYSICAL_ADDR, and suitable for containing the kernel. EFI stub will perform a kernel relocation when condition 1 is met. But due to condition 2, EFI stub can't relocate kernel to the preferred address, so it fallback to ask EFI firmware to alloc lowest usable memory region, got the low region mentioned in condition 3, and relocated kernel there. It's incorrect to relocate the kernel below LOAD_PHYSICAL_ADDR. This is the lowest acceptable kernel relocation address. The first thing goes wrong is in arch/x86/boot/compressed/head_64.S. Kernel decompression will force use LOAD_PHYSICAL_ADDR as the output address if kernel is located below it. Then the relocation before decompression, which move kernel to the end of the decompression buffer, will overwrite other memory region, as there is no enough memory there. To fix it, just don't let EFI stub relocate the kernel to any address lower than lowest acceptable address. [ ardb: introduce efi_low_alloc_above() to reduce the scope of the change ] Signed-off-by: Kairui Song Signed-off-by: Ard Biesheuvel Acked-by: Jarkko Sakkinen Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: linux-efi@vger.kernel.org Link: https://lkml.kernel.org/r/20191029173755.27149-6-ardb@kernel.org Signed-off-by: Ingo Molnar --- include/linux/efi.h | 18 ++++++++++++++++-- 1 file changed, 16 insertions(+), 2 deletions(-) (limited to 'include') diff --git a/include/linux/efi.h b/include/linux/efi.h index bd3837022307..d87acf62958e 100644 --- a/include/linux/efi.h +++ b/include/linux/efi.h @@ -1579,9 +1579,22 @@ char *efi_convert_cmdline(efi_system_table_t *sys_table_arg, efi_status_t efi_get_memory_map(efi_system_table_t *sys_table_arg, struct efi_boot_memmap *map); +efi_status_t efi_low_alloc_above(efi_system_table_t *sys_table_arg, + unsigned long size, unsigned long align, + unsigned long *addr, unsigned long min); + +static inline efi_status_t efi_low_alloc(efi_system_table_t *sys_table_arg, unsigned long size, unsigned long align, - unsigned long *addr); + unsigned long *addr) +{ + /* + * Don't allocate at 0x0. It will confuse code that + * checks pointers against NULL. Skip the first 8 + * bytes so we start at a nice even number. + */ + return efi_low_alloc_above(sys_table_arg, size, align, addr, 0x8); +} efi_status_t efi_high_alloc(efi_system_table_t *sys_table_arg, unsigned long size, unsigned long align, @@ -1592,7 +1605,8 @@ efi_status_t efi_relocate_kernel(efi_system_table_t *sys_table_arg, unsigned long image_size, unsigned long alloc_size, unsigned long preferred_addr, - unsigned long alignment); + unsigned long alignment, + unsigned long min_addr); efi_status_t handle_cmdline_files(efi_system_table_t *sys_table_arg, efi_loaded_image_t *image, -- cgit v1.2.3 From 359efcc2c910117d2faf704ce154e91fc976d37f Mon Sep 17 00:00:00 2001 From: Javier Martinez Canillas Date: Tue, 29 Oct 2019 18:37:55 +0100 Subject: efi/efi_test: Lock down /dev/efi_test and require CAP_SYS_ADMIN The driver exposes EFI runtime services to user-space through an IOCTL interface, calling the EFI services function pointers directly without using the efivar API. Disallow access to the /dev/efi_test character device when the kernel is locked down to prevent arbitrary user-space to call EFI runtime services. Also require CAP_SYS_ADMIN to open the chardev to prevent unprivileged users to call the EFI runtime services, instead of just relying on the chardev file mode bits for this. The main user of this driver is the fwts [0] tool that already checks if the effective user ID is 0 and fails otherwise. So this change shouldn't cause any regression to this tool. [0]: https://wiki.ubuntu.com/FirmwareTestSuite/Reference/uefivarinfo Signed-off-by: Javier Martinez Canillas Signed-off-by: Ard Biesheuvel Acked-by: Laszlo Ersek Acked-by: Matthew Garrett Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: linux-efi@vger.kernel.org Link: https://lkml.kernel.org/r/20191029173755.27149-7-ardb@kernel.org Signed-off-by: Ingo Molnar --- drivers/firmware/efi/test/efi_test.c | 8 ++++++++ include/linux/security.h | 1 + security/lockdown/lockdown.c | 1 + 3 files changed, 10 insertions(+) (limited to 'include') diff --git a/drivers/firmware/efi/test/efi_test.c b/drivers/firmware/efi/test/efi_test.c index 877745c3aaf2..7baf48c01e72 100644 --- a/drivers/firmware/efi/test/efi_test.c +++ b/drivers/firmware/efi/test/efi_test.c @@ -14,6 +14,7 @@ #include #include #include +#include #include #include @@ -717,6 +718,13 @@ static long efi_test_ioctl(struct file *file, unsigned int cmd, static int efi_test_open(struct inode *inode, struct file *file) { + int ret = security_locked_down(LOCKDOWN_EFI_TEST); + + if (ret) + return ret; + + if (!capable(CAP_SYS_ADMIN)) + return -EACCES; /* * nothing special to do here * We do accept multiple open files at the same time as we diff --git a/include/linux/security.h b/include/linux/security.h index a8d59d612d27..9df7547afc0c 100644 --- a/include/linux/security.h +++ b/include/linux/security.h @@ -105,6 +105,7 @@ enum lockdown_reason { LOCKDOWN_NONE, LOCKDOWN_MODULE_SIGNATURE, LOCKDOWN_DEV_MEM, + LOCKDOWN_EFI_TEST, LOCKDOWN_KEXEC, LOCKDOWN_HIBERNATION, LOCKDOWN_PCI_ACCESS, diff --git a/security/lockdown/lockdown.c b/security/lockdown/lockdown.c index 8a10b43daf74..40b790536def 100644 --- a/security/lockdown/lockdown.c +++ b/security/lockdown/lockdown.c @@ -20,6 +20,7 @@ static const char *const lockdown_reasons[LOCKDOWN_CONFIDENTIALITY_MAX+1] = { [LOCKDOWN_NONE] = "none", [LOCKDOWN_MODULE_SIGNATURE] = "unsigned module loading", [LOCKDOWN_DEV_MEM] = "/dev/mem,kmem,port", + [LOCKDOWN_EFI_TEST] = "/dev/efi_test access", [LOCKDOWN_KEXEC] = "kexec of unsigned images", [LOCKDOWN_HIBERNATION] = "hibernation", [LOCKDOWN_PCI_ACCESS] = "direct PCI access", -- cgit v1.2.3