diff options
Diffstat (limited to 'arch/x86/kernel/cpu/common.c')
| -rw-r--r-- | arch/x86/kernel/cpu/common.c | 33 |
1 files changed, 26 insertions, 7 deletions
diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c index a8ff4376c286..ec0670114efa 100644 --- a/arch/x86/kernel/cpu/common.c +++ b/arch/x86/kernel/cpu/common.c @@ -433,7 +433,20 @@ static __always_inline void setup_lass(struct cpuinfo_x86 *c) /* These bits should not change their value after CPU init is finished. */ static const unsigned long cr4_pinned_mask = X86_CR4_SMEP | X86_CR4_SMAP | X86_CR4_UMIP | - X86_CR4_FSGSBASE | X86_CR4_CET | X86_CR4_FRED; + X86_CR4_FSGSBASE | X86_CR4_CET; + +/* + * The CR pinning protects against ROP on the 'mov %reg, %CRn' instruction(s). + * Since you can ROP directly to these instructions (barring shadow stack), + * any protection must follow immediately and unconditionally after that. + * + * Specifically, the CR[04] write functions below will have the value + * validation controlled by the @cr_pinning static_branch which is + * __ro_after_init, just like the cr4_pinned_bits value. + * + * Once set, an attacker will have to defeat page-tables to get around these + * restrictions. Which is a much bigger ask than 'simple' ROP. + */ static DEFINE_STATIC_KEY_FALSE_RO(cr_pinning); static unsigned long cr4_pinned_bits __ro_after_init; @@ -2050,12 +2063,6 @@ static void identify_cpu(struct cpuinfo_x86 *c) setup_umip(c); setup_lass(c); - /* Enable FSGSBASE instructions if available. */ - if (cpu_has(c, X86_FEATURE_FSGSBASE)) { - cr4_set_bits(X86_CR4_FSGSBASE); - elf_hwcap2 |= HWCAP2_FSGSBASE; - } - /* * The vendor-specific functions might have changed features. * Now we do "generic changes." @@ -2416,6 +2423,18 @@ void cpu_init_exception_handling(bool boot_cpu) /* GHCB needs to be setup to handle #VC. */ setup_ghcb(); + /* + * On CPUs with FSGSBASE support, paranoid_entry() uses + * ALTERNATIVE-patched RDGSBASE/WRGSBASE instructions. Secondary CPUs + * boot after alternatives are patched globally, so early exceptions + * execute patched code that depends on FSGSBASE. Enable the feature + * before any exceptions occur. + */ + if (cpu_feature_enabled(X86_FEATURE_FSGSBASE)) { + cr4_set_bits(X86_CR4_FSGSBASE); + elf_hwcap2 |= HWCAP2_FSGSBASE; + } + if (cpu_feature_enabled(X86_FEATURE_FRED)) { /* The boot CPU has enabled FRED during early boot */ if (!boot_cpu) |