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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [Xen-devel] [PATCH v1 3/6] x86: Enable Supervisor Mode Execution Prevention (SMAP) for Xen
Supervisor Mode Access Prevention (SMAP) is a new security feature disclosed by Intel, please refer to the following document: http://software.intel.com/sites/default/files/319433-014.pdf If CR4.SMAP = 1, supervisor-mode data accesses are not allowed to linear addresses that are accessible in user mode. If CPL < 3, SMAP protections are disabled if EFLAGS.AC = 1. If CPL = 3, SMAP applies to all supervisor-mode data accesses (these are implicit supervisor accesses) regardless of the value of EFLAGS.AC. This patch enables SMAP in Xen to prevent Xen hypervisor from accessing pv guest data, whose translation paging-structure entries' U/S flags are all set. Signed-off-by: Feng Wu <feng.wu@xxxxxxxxx> --- xen/arch/x86/setup.c | 9 +++++++++ xen/arch/x86/traps.c | 34 ++++++++++++++++++++++++++-------- xen/include/asm-x86/cpufeature.h | 1 + xen/include/asm-x86/domain.h | 6 ++++-- 4 files changed, 40 insertions(+), 10 deletions(-) diff --git a/xen/arch/x86/setup.c b/xen/arch/x86/setup.c index e9c2c51..09c974d 100644 --- a/xen/arch/x86/setup.c +++ b/xen/arch/x86/setup.c @@ -61,6 +61,10 @@ integer_param("maxcpus", max_cpus); static bool_t __initdata disable_smep; invbool_param("smep", disable_smep); +/* smap: Enable/disable Supervisor Mode Access Prevention (default on). */ +static bool_t __initdata disable_smap; +invbool_param("smap", disable_smap); + /* **** Linux config option: propagated to domain0. */ /* "acpi=off": Sisables both ACPI table parsing and interpreter. */ /* "acpi=force": Override the disable blacklist. */ @@ -1279,6 +1283,11 @@ void __init noreturn __start_xen(unsigned long mbi_p) if ( cpu_has_smep ) set_in_cr4(X86_CR4_SMEP); + if ( disable_smap ) + setup_clear_cpu_cap(X86_FEATURE_SMAP); + if ( cpu_has_smap ) + set_in_cr4(X86_CR4_SMAP); + if ( cpu_has_fsgsbase ) set_in_cr4(X86_CR4_FSGSBASE); diff --git a/xen/arch/x86/traps.c b/xen/arch/x86/traps.c index ed4ae2d..9307f10 100644 --- a/xen/arch/x86/traps.c +++ b/xen/arch/x86/traps.c @@ -1182,11 +1182,12 @@ static int handle_gdt_ldt_mapping_fault( enum pf_type { real_fault, smep_fault, + smap_fault, spurious_fault }; static enum pf_type __page_fault_type( - unsigned long addr, unsigned int error_code) + unsigned long addr, struct cpu_user_regs *regs) { unsigned long mfn, cr3 = read_cr3(); l4_pgentry_t l4e, *l4t; @@ -1194,6 +1195,7 @@ static enum pf_type __page_fault_type( l2_pgentry_t l2e, *l2t; l1_pgentry_t l1e, *l1t; unsigned int required_flags, disallowed_flags, page_user; + unsigned int error_code = regs->error_code; /* * We do not take spurious page faults in IRQ handlers as we do not @@ -1270,11 +1272,26 @@ leaf: ((error_code & (PFEC_insn_fetch|PFEC_user_mode)) == PFEC_insn_fetch) ) return smep_fault; + /* + * Supervisor Mode Access Prevention (SMAP): + * Disallow supervisor access user-accessible mappings + * A fault is considered as an SMAP violation if the following + * conditions are ture: + * - X86_CR4_SMAP is set in CR4 + * - An user page is accessed + * - CPL=3 or X86_EFLAGS_AC is clear + * - Page fault in kernel mode + */ + if ( (read_cr4() & X86_CR4_SMAP) && page_user && + !(((regs->cs & 0x03) < 3) && (regs->eflags & X86_EFLAGS_AC)) && + !(error_code & PFEC_user_mode) ) + return smap_fault; + return spurious_fault; } static enum pf_type spurious_page_fault( - unsigned long addr, unsigned int error_code) + unsigned long addr, struct cpu_user_regs *regs) { unsigned long flags; enum pf_type pf_type; @@ -1284,7 +1301,7 @@ static enum pf_type spurious_page_fault( * page tables from becoming invalid under our feet during the walk. */ local_irq_save(flags); - pf_type = __page_fault_type(addr, error_code); + pf_type = __page_fault_type(addr, regs); local_irq_restore(flags); return pf_type; @@ -1379,8 +1396,8 @@ void do_page_fault(struct cpu_user_regs *regs) if ( unlikely(!guest_mode(regs)) ) { - pf_type = spurious_page_fault(addr, error_code); - BUG_ON(pf_type == smep_fault); + pf_type = spurious_page_fault(addr, regs); + BUG_ON((pf_type == smep_fault) || (pf_type == smap_fault)); if ( pf_type != real_fault ) return; @@ -1406,10 +1423,11 @@ void do_page_fault(struct cpu_user_regs *regs) if ( unlikely(current->domain->arch.suppress_spurious_page_faults) ) { - pf_type = spurious_page_fault(addr, error_code); - if ( pf_type == smep_fault ) + pf_type = spurious_page_fault(addr, regs); + if ( (pf_type == smep_fault) || (pf_type == smap_fault)) { - gdprintk(XENLOG_ERR, "Fatal SMEP fault\n"); + gdprintk(XENLOG_ERR, "Fatal %s fault\n", + (pf_type == smep_fault) ? "SMEP" : "SMAP"); domain_crash(current->domain); } if ( pf_type != real_fault ) diff --git a/xen/include/asm-x86/cpufeature.h b/xen/include/asm-x86/cpufeature.h index 0c4d6c1..3ded6bd 100644 --- a/xen/include/asm-x86/cpufeature.h +++ b/xen/include/asm-x86/cpufeature.h @@ -186,6 +186,7 @@ #define cpu_has_fsgsbase boot_cpu_has(X86_FEATURE_FSGSBASE) #define cpu_has_smep boot_cpu_has(X86_FEATURE_SMEP) +#define cpu_has_smap boot_cpu_has(X86_FEATURE_SMAP) #define cpu_has_fpu_sel (!boot_cpu_has(X86_FEATURE_NO_FPU_SEL)) #define cpu_has_ffxsr ((boot_cpu_data.x86_vendor == X86_VENDOR_AMD) \ diff --git a/xen/include/asm-x86/domain.h b/xen/include/asm-x86/domain.h index 4ff89f0..3b515f2 100644 --- a/xen/include/asm-x86/domain.h +++ b/xen/include/asm-x86/domain.h @@ -464,12 +464,14 @@ unsigned long pv_guest_cr4_fixup(const struct vcpu *, unsigned long guest_cr4); (((v)->arch.pv_vcpu.ctrlreg[4] \ | (mmu_cr4_features \ & (X86_CR4_PGE | X86_CR4_PSE | X86_CR4_SMEP | \ - X86_CR4_OSXSAVE | X86_CR4_FSGSBASE)) \ + X86_CR4_SMAP | X86_CR4_OSXSAVE | \ + X86_CR4_FSGSBASE)) \ | ((v)->domain->arch.vtsc ? X86_CR4_TSD : 0)) \ & ~X86_CR4_DE) #define real_cr4_to_pv_guest_cr4(c) \ ((c) & ~(X86_CR4_PGE | X86_CR4_PSE | X86_CR4_TSD | \ - X86_CR4_OSXSAVE | X86_CR4_SMEP | X86_CR4_FSGSBASE)) + X86_CR4_OSXSAVE | X86_CR4_SMEP | \ + X86_CR4_FSGSBASE | X86_CR4_SMAP)) void domain_cpuid(struct domain *d, unsigned int input, -- 1.8.3.1 _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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