diff options
Diffstat (limited to 'arch/x86/coco/core.c')
| -rw-r--r-- | arch/x86/coco/core.c | 53 |
1 files changed, 42 insertions, 11 deletions
diff --git a/arch/x86/coco/core.c b/arch/x86/coco/core.c index 49b44f881..801e943fd 100644 --- a/arch/x86/coco/core.c +++ b/arch/x86/coco/core.c @@ -3,18 +3,22 @@ * Confidential Computing Platform Capability checks * * Copyright (C) 2021 Advanced Micro Devices, Inc. + * Copyright (C) 2024 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved. * * Author: Tom Lendacky <thomas.lendacky@amd.com> */ #include <linux/export.h> #include <linux/cc_platform.h> +#include <linux/string.h> +#include <linux/random.h> +#include <asm/archrandom.h> #include <asm/coco.h> #include <asm/processor.h> -static enum cc_vendor vendor __ro_after_init; -static u64 cc_mask __ro_after_init; +enum cc_vendor cc_vendor __ro_after_init = CC_VENDOR_NONE; +u64 cc_mask __ro_after_init; static bool intel_cc_platform_has(enum cc_attr attr) { @@ -83,7 +87,7 @@ static bool hyperv_cc_platform_has(enum cc_attr attr) bool cc_platform_has(enum cc_attr attr) { - switch (vendor) { + switch (cc_vendor) { case CC_VENDOR_AMD: return amd_cc_platform_has(attr); case CC_VENDOR_INTEL: @@ -105,7 +109,7 @@ u64 cc_mkenc(u64 val) * - for AMD, bit *set* means the page is encrypted * - for Intel *clear* means encrypted. */ - switch (vendor) { + switch (cc_vendor) { case CC_VENDOR_AMD: return val | cc_mask; case CC_VENDOR_INTEL: @@ -118,7 +122,7 @@ u64 cc_mkenc(u64 val) u64 cc_mkdec(u64 val) { /* See comment in cc_mkenc() */ - switch (vendor) { + switch (cc_vendor) { case CC_VENDOR_AMD: return val & ~cc_mask; case CC_VENDOR_INTEL: @@ -129,12 +133,39 @@ u64 cc_mkdec(u64 val) } EXPORT_SYMBOL_GPL(cc_mkdec); -__init void cc_set_vendor(enum cc_vendor v) +__init void cc_random_init(void) { - vendor = v; -} + /* + * The seed is 32 bytes (in units of longs), which is 256 bits, which + * is the security level that the RNG is targeting. + */ + unsigned long rng_seed[32 / sizeof(long)]; + size_t i, longs; -__init void cc_set_mask(u64 mask) -{ - cc_mask = mask; + if (!cc_platform_has(CC_ATTR_GUEST_MEM_ENCRYPT)) + return; + + /* + * Since the CoCo threat model includes the host, the only reliable + * source of entropy that can be neither observed nor manipulated is + * RDRAND. Usually, RDRAND failure is considered tolerable, but since + * CoCo guests have no other unobservable source of entropy, it's + * important to at least ensure the RNG gets some initial random seeds. + */ + for (i = 0; i < ARRAY_SIZE(rng_seed); i += longs) { + longs = arch_get_random_longs(&rng_seed[i], ARRAY_SIZE(rng_seed) - i); + + /* + * A zero return value means that the guest doesn't have RDRAND + * or the CPU is physically broken, and in both cases that + * means most crypto inside of the CoCo instance will be + * broken, defeating the purpose of CoCo in the first place. So + * just panic here because it's absolutely unsafe to continue + * executing. + */ + if (longs == 0) + panic("RDRAND is defective."); + } + add_device_randomness(rng_seed, sizeof(rng_seed)); + memzero_explicit(rng_seed, sizeof(rng_seed)); } |