[PATCH v8 04/27] x86/fpu/xstate: Introduce XSAVES system states

Yu-cheng Yu
2019-08-13T20:52:02Z

Control-flow Enforcement (CET) MSR contents are XSAVES system states.
To support CET, introduce XSAVES system states first.

Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
---
arch/x86/include/asm/fpu/internal.h | 23 +++++++-
arch/x86/include/asm/fpu/xstate.h | 4 +-
arch/x86/kernel/fpu/core.c | 26 +++++++--
arch/x86/kernel/fpu/init.c | 10 ----
arch/x86/kernel/fpu/signal.c | 4 +-
arch/x86/kernel/fpu/xstate.c | 90 +++++++++++++++++++----------
arch/x86/kernel/process.c | 2 +-
arch/x86/kernel/signal.c | 2 +-
8 files changed, 106 insertions(+), 55 deletions(-)

diff --git a/arch/x86/include/asm/fpu/internal.h b/arch/x86/include/asm/fpu/internal.h
index 652be3853b40..2ca5c36a77d5 100644
--- a/arch/x86/include/asm/fpu/internal.h
+++ b/arch/x86/include/asm/fpu/internal.h
@@ -31,7 +31,8 @@ extern void fpu__save(struct fpu *fpu);
extern int fpu__restore_sig(void __user *buf, int ia32_frame);
extern void fpu__drop(struct fpu *fpu);
extern int fpu__copy(struct task_struct *dst, struct task_struct *src);
-extern void fpu__clear(struct fpu *fpu);
+extern void fpu__clear_user_states(struct fpu *fpu);
+extern void fpu__clear_all(struct fpu *fpu);
extern int fpu__exception_code(struct fpu *fpu, int trap_nr);
extern int dump_fpu(struct pt_regs *ptregs, struct user_i387_struct *fpstate);

@@ -44,7 +45,6 @@ extern void fpu__init_cpu_xstate(void);
extern void fpu__init_system(struct cpuinfo_x86 *c);
extern void fpu__init_check_bugs(void);
extern void fpu__resume_cpu(void);
-extern u64 fpu__get_supported_xfeatures_mask(void);

/*
* Debugging facility:
@@ -92,7 +92,7 @@ static inline void fpstate_init_xstate(struct xregs_state *xsave)
* XRSTORS requires these bits set in xcomp_bv, or it will
* trigger #GP:
*/
- xsave->header.xcomp_bv = XCOMP_BV_COMPACTED_FORMAT | xfeatures_mask_user;
+ xsave->header.xcomp_bv = XCOMP_BV_COMPACTED_FORMAT | xfeatures_mask_all;
}

static inline void fpstate_init_fxstate(struct fxregs_state *fx)
@@ -615,6 +615,23 @@ static inline void switch_fpu_finish(struct fpu *new_fpu)
__write_pkru(pkru_val);
}

+/*
+ * On context switches, XSAVE states are not restored until returning
+ * to user-mode. FPU registers need to be restored before any changes,
+ * and protected by fpregs_lock()/fpregs_unlock().
+ */
+static inline void modify_fpu_regs_begin(void)
+{
+ fpregs_lock();
+ if (test_thread_flag(TIF_NEED_FPU_LOAD))
+ __fpregs_load_activate();
+}
+
+static inline void modify_fpu_regs_end(void)
+{
+ fpregs_unlock();
+}
+
/*
* MXCSR and XCR definitions:
*/
diff --git a/arch/x86/include/asm/fpu/xstate.h b/arch/x86/include/asm/fpu/xstate.h
index 9ded9532257d..970bbd303cfb 100644
--- a/arch/x86/include/asm/fpu/xstate.h
+++ b/arch/x86/include/asm/fpu/xstate.h
@@ -21,9 +21,6 @@
#define XSAVE_YMM_SIZE 256
#define XSAVE_YMM_OFFSET (XSAVE_HDR_SIZE + XSAVE_HDR_OFFSET)

-/* Supervisor features */
-#define XFEATURE_MASK_SUPERVISOR (XFEATURE_MASK_PT)
-
/* All currently supported features */
#define SUPPORTED_XFEATURES_MASK (XFEATURE_MASK_FP | \
XFEATURE_MASK_SSE | \
@@ -42,6 +39,7 @@
#endif

extern u64 xfeatures_mask_user;
+extern u64 xfeatures_mask_all;
extern u64 xstate_fx_sw_bytes[USER_XSTATE_FX_SW_WORDS];

extern void __init update_regset_xstate_info(unsigned int size,
diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
index 12c70840980e..31d3cd70b5df 100644
--- a/arch/x86/kernel/fpu/core.c
+++ b/arch/x86/kernel/fpu/core.c
@@ -294,12 +294,16 @@ void fpu__drop(struct fpu *fpu)
* Clear FPU registers by setting them up from
* the init fpstate:
*/
-static inline void copy_init_fpstate_to_fpregs(void)
+static inline void copy_init_fpstate_to_fpregs(u64 features_mask)
{
fpregs_lock();

+ /*
+ * Only XSAVES user states are copied.
+ * System states are preserved.
+ */
if (use_xsave())
- copy_kernel_to_xregs(&init_fpstate.xsave, -1);
+ copy_kernel_to_xregs(&init_fpstate.xsave, features_mask);
else if (static_cpu_has(X86_FEATURE_FXSR))
copy_kernel_to_fxregs(&init_fpstate.fxsave);
else
@@ -318,7 +322,21 @@ static inline void copy_init_fpstate_to_fpregs(void)
* Called by sys_execve(), by the signal handler code and by various
* error paths.
*/
-void fpu__clear(struct fpu *fpu)
+void fpu__clear_user_states(struct fpu *fpu)
+{
+ WARN_ON_FPU(fpu != &current->thread.fpu); /* Almost certainly an anomaly */
+
+ fpu__drop(fpu);
+
+ /*
+ * Make sure fpstate is cleared and initialized.
+ */
+ fpu__initialize(fpu);
+ if (static_cpu_has(X86_FEATURE_FPU))
+ copy_init_fpstate_to_fpregs(xfeatures_mask_user);
+}
+
+void fpu__clear_all(struct fpu *fpu)
{
WARN_ON_FPU(fpu != &current->thread.fpu); /* Almost certainly an anomaly */

@@ -329,7 +347,7 @@ void fpu__clear(struct fpu *fpu)
*/
fpu__initialize(fpu);
if (static_cpu_has(X86_FEATURE_FPU))
- copy_init_fpstate_to_fpregs();
+ copy_init_fpstate_to_fpregs(xfeatures_mask_all);
}

/*
diff --git a/arch/x86/kernel/fpu/init.c b/arch/x86/kernel/fpu/init.c
index 73fed33e5bda..0a0ba584a533 100644
--- a/arch/x86/kernel/fpu/init.c
+++ b/arch/x86/kernel/fpu/init.c
@@ -217,16 +217,6 @@ static void __init fpu__init_system_xstate_size_legacy(void)
fpu_user_xstate_size = fpu_kernel_xstate_size;
}

-/*
- * Find supported xfeatures based on cpu features and command-line input.
- * This must be called after fpu__init_parse_early_param() is called and
- * xfeatures_mask is enumerated.
- */
-u64 __init fpu__get_supported_xfeatures_mask(void)
-{
- return SUPPORTED_XFEATURES_MASK;
-}
-
/* Legacy code to initialize eager fpu mode. */
static void __init fpu__init_system_ctx_switch(void)
{
diff --git a/arch/x86/kernel/fpu/signal.c b/arch/x86/kernel/fpu/signal.c
index 8a63f07cf400..4ecf1764a971 100644
--- a/arch/x86/kernel/fpu/signal.c
+++ b/arch/x86/kernel/fpu/signal.c
@@ -285,7 +285,7 @@ static int __fpu__restore_sig(void __user *buf, void __user *buf_fx, int size)
IS_ENABLED(CONFIG_IA32_EMULATION));

if (!buf) {
- fpu__clear(fpu);
+ fpu__clear_user_states(fpu);
return 0;
}

@@ -407,7 +407,7 @@ static int __fpu__restore_sig(void __user *buf, void __user *buf_fx, int size)

err_out:
if (ret)
- fpu__clear(fpu);
+ fpu__clear_user_states(fpu);
return ret;
}

diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c
index d560e8861a3c..9fbe73c546df 100644
--- a/arch/x86/kernel/fpu/xstate.c
+++ b/arch/x86/kernel/fpu/xstate.c
@@ -61,9 +61,19 @@ static short xsave_cpuid_features[] __initdata = {
*/
u64 xfeatures_mask_user __read_mostly;

+/*
+ * Supported XSAVES system states.
+ */
+static u64 xfeatures_mask_system __read_mostly;
+
+/*
+ * Combined XSAVES system and user states.
+ */
+u64 xfeatures_mask_all __read_mostly;
+
static unsigned int xstate_offsets[XFEATURE_MAX] = { [ 0 ... XFEATURE_MAX - 1] = -1};
static unsigned int xstate_sizes[XFEATURE_MAX] = { [ 0 ... XFEATURE_MAX - 1] = -1};
-static unsigned int xstate_comp_offsets[sizeof(xfeatures_mask_user)*8];
+static unsigned int xstate_comp_offsets[sizeof(xfeatures_mask_all)*8];

/*
* The XSAVE area of kernel can be in standard or compacted format;
@@ -79,7 +89,7 @@ unsigned int fpu_user_xstate_size;
*/
int cpu_has_xfeatures(u64 xfeatures_needed, const char **feature_name)
{
- u64 xfeatures_missing = xfeatures_needed & ~xfeatures_mask_user;
+ u64 xfeatures_missing = xfeatures_needed & ~xfeatures_mask_all;

if (unlikely(feature_name)) {
long xfeature_idx, max_idx;
@@ -158,7 +168,7 @@ void fpstate_sanitize_xstate(struct fpu *fpu)
* None of the feature bits are in init state. So nothing else
* to do for us, as the memory layout is up to date.
*/
- if ((xfeatures & xfeatures_mask_user) == xfeatures_mask_user)
+ if ((xfeatures & xfeatures_mask_all) == xfeatures_mask_all)
return;

/*
@@ -213,28 +223,27 @@ void fpstate_sanitize_xstate(struct fpu *fpu)
*/
void fpu__init_cpu_xstate(void)
{
- if (!boot_cpu_has(X86_FEATURE_XSAVE) || !xfeatures_mask_user)
+ if (!boot_cpu_has(X86_FEATURE_XSAVE) || !xfeatures_mask_all)
return;
/*
* XCR_XFEATURE_ENABLED_MASK sets the features that are managed
* by XSAVE{C, OPT} and XRSTOR. Only XSAVE user states can be
* set here.
*/
-
- xfeatures_mask_user &= ~XFEATURE_MASK_SUPERVISOR;
-
cr4_set_bits(X86_CR4_OSXSAVE);
xsetbv(XCR_XFEATURE_ENABLED_MASK, xfeatures_mask_user);
+
+ /*
+ * MSR_IA32_XSS controls which system (not user) states are
+ * to be managed by XSAVES.
+ */
+ if (boot_cpu_has(X86_FEATURE_XSAVES))
+ wrmsrl(MSR_IA32_XSS, xfeatures_mask_system);
}

-/*
- * Note that in the future we will likely need a pair of
- * functions here: one for user xstates and the other for
- * system xstates. For now, they are the same.
- */
static int xfeature_enabled(enum xfeature xfeature)
{
- return !!(xfeatures_mask_user & BIT_ULL(xfeature));
+ return !!(xfeatures_mask_all & BIT_ULL(xfeature));
}

/*
@@ -340,7 +349,7 @@ static int xfeature_is_aligned(int xfeature_nr)
*/
static void __init setup_xstate_comp(void)
{
- unsigned int xstate_comp_sizes[sizeof(xfeatures_mask_user)*8];
+ unsigned int xstate_comp_sizes[sizeof(xfeatures_mask_all)*8];
int i;

/*
@@ -413,7 +422,7 @@ static void __init setup_init_fpu_buf(void)
print_xstate_features();

if (boot_cpu_has(X86_FEATURE_XSAVES))
- init_fpstate.xsave.header.xcomp_bv = BIT_ULL(63) | xfeatures_mask_user;
+ init_fpstate.xsave.header.xcomp_bv = BIT_ULL(63) | xfeatures_mask_all;

/*
* Init all the features state with header.xfeatures being 0x0
@@ -436,7 +445,7 @@ static int xfeature_uncompacted_offset(int xfeature_nr)
* format. Checking a system state's uncompacted offset is
* an error.
*/
- if (XFEATURE_MASK_SUPERVISOR & BIT_ULL(xfeature_nr)) {
+ if (~xfeatures_mask_user & BIT_ULL(xfeature_nr)) {
WARN_ONCE(1, "No fixed offset for xstate %d\n", xfeature_nr);
return -1;
}
@@ -608,15 +617,12 @@ static void do_extra_xstate_size_checks(void)

/*
- * Get total size of enabled xstates in XCR0/xfeatures_mask_user.
+ * Get total size of enabled xstates in XCR0 | IA32_XSS.
*
* Note the SDM's wording here. "sub-function 0" only enumerates
* the size of the *user* states. If we use it to size a buffer
* that we use 'XSAVES' on, we could potentially overflow the
* buffer because 'XSAVES' saves system states too.
- *
- * Note that we do not currently set any bits on IA32_XSS so
- * 'XCR0 | IA32_XSS == XCR0' for now.
*/
static unsigned int __init get_xsaves_size(void)
{
@@ -698,6 +704,7 @@ static int __init init_xstate_size(void)
*/
static void fpu__init_disable_system_xstate(void)
{
+ xfeatures_mask_all = 0;
xfeatures_mask_user = 0;
cr4_clear_bits(X86_CR4_OSXSAVE);
setup_clear_cpu_cap(X86_FEATURE_XSAVE);
@@ -733,10 +740,23 @@ void __init fpu__init_system_xstate(void)
return;
}

+ /*
+ * Find user states supported by the processor.
+ * Only these bits can be set in XCR0.
+ */
cpuid_count(XSTATE_CPUID, 0, &eax, &ebx, &ecx, &edx);
xfeatures_mask_user = eax + ((u64)edx << 32);

- if ((xfeatures_mask_user & XFEATURE_MASK_FPSSE) != XFEATURE_MASK_FPSSE) {
+ /*
+ * Find system states supported by the processor.
+ * Only these bits can be set in IA32_XSS MSR.
+ */
+ cpuid_count(XSTATE_CPUID, 1, &eax, &ebx, &ecx, &edx);
+ xfeatures_mask_system = ecx + ((u64)edx << 32);
+
+ xfeatures_mask_all = xfeatures_mask_user | xfeatures_mask_system;
+
+ if ((xfeatures_mask_all & XFEATURE_MASK_FPSSE) != XFEATURE_MASK_FPSSE) {
/*
* This indicates that something really unexpected happened
* with the enumeration. Disable XSAVE and try to continue
@@ -751,10 +771,12 @@ void __init fpu__init_system_xstate(void)
*/
for (i = 0; i < ARRAY_SIZE(xsave_cpuid_features); i++) {
if (!boot_cpu_has(xsave_cpuid_features[i]))
- xfeatures_mask_user &= ~BIT_ULL(i);
+ xfeatures_mask_all &= ~BIT_ULL(i);
}

- xfeatures_mask_user &= fpu__get_supported_xfeatures_mask();
+ xfeatures_mask_all &= SUPPORTED_XFEATURES_MASK;
+ xfeatures_mask_user &= xfeatures_mask_all;
+ xfeatures_mask_system &= xfeatures_mask_all;

/* Enable xstate instructions to be able to continue with initialization: */
fpu__init_cpu_xstate();
@@ -766,7 +788,7 @@ void __init fpu__init_system_xstate(void)
* Update info used for ptrace frames; use standard-format size and no
* system xstates:
*/
- update_regset_xstate_info(fpu_user_xstate_size, xfeatures_mask_user & ~XFEATURE_MASK_SUPERVISOR);
+ update_regset_xstate_info(fpu_user_xstate_size, xfeatures_mask_user);

fpu__init_prepare_fx_sw_frame();
setup_init_fpu_buf();
@@ -774,7 +796,7 @@ void __init fpu__init_system_xstate(void)
print_xstate_offset_size();

pr_info("x86/fpu: Enabled xstate features 0x%llx, context size is %d bytes, using '%s' format.\n",
- xfeatures_mask_user,
+ xfeatures_mask_all,
fpu_kernel_xstate_size,
boot_cpu_has(X86_FEATURE_XSAVES) ? "compacted" : "standard");
return;
@@ -794,6 +816,12 @@ void fpu__resume_cpu(void)
*/
if (boot_cpu_has(X86_FEATURE_XSAVE))
xsetbv(XCR_XFEATURE_ENABLED_MASK, xfeatures_mask_user);
+
+ /*
+ * Restore IA32_XSS
+ */
+ if (boot_cpu_has(X86_FEATURE_XSAVES))
+ wrmsrl(MSR_IA32_XSS, xfeatures_mask_system);
}

/*
@@ -839,9 +867,9 @@ void *get_xsave_addr(struct xregs_state *xsave, int xfeature_nr)
/*
* We should not ever be requesting features that we
* have not enabled. Remember that pcntxt_mask is
- * what we write to the XCR0 register.
+ * what we write to the XCR0 | IA32_XSS registers.
*/
- WARN_ONCE(!(xfeatures_mask_user & BIT_ULL(xfeature_nr)),
+ WARN_ONCE(!(xfeatures_mask_all & BIT_ULL(xfeature_nr)),
"get of unsupported state");
/*
* This assumes the last 'xsave*' instruction to
@@ -989,7 +1017,7 @@ int copy_xstate_to_kernel(void *kbuf, struct xregs_state *xsave, unsigned int of
*/
memset(&header, 0, sizeof(header));
header.xfeatures = xsave->header.xfeatures;
- header.xfeatures &= ~XFEATURE_MASK_SUPERVISOR;
+ header.xfeatures &= xfeatures_mask_user;

/*
* Copy xregs_state->header:
@@ -1073,7 +1101,7 @@ int copy_xstate_to_user(void __user *ubuf, struct xregs_state *xsave, unsigned i
*/
memset(&header, 0, sizeof(header));
header.xfeatures = xsave->header.xfeatures;
- header.xfeatures &= ~XFEATURE_MASK_SUPERVISOR;
+ header.xfeatures &= xfeatures_mask_user;

/*
* Copy xregs_state->header:
@@ -1166,7 +1194,7 @@ int copy_kernel_to_xstate(struct xregs_state *xsave, const void *kbuf)
* The state that came in from userspace was user-state only.
* Mask all the user states out of 'xfeatures':
*/
- xsave->header.xfeatures &= XFEATURE_MASK_SUPERVISOR;
+ xsave->header.xfeatures &= xfeatures_mask_system;

/*
* Add back in the features that came in from userspace:
@@ -1222,7 +1250,7 @@ int copy_user_to_xstate(struct xregs_state *xsave, const void __user *ubuf)
* The state that came in from userspace was user-state only.
* Mask all the user states out of 'xfeatures':
*/
- xsave->header.xfeatures &= XFEATURE_MASK_SUPERVISOR;
+ xsave->header.xfeatures &= xfeatures_mask_system;

/*
* Add back in the features that came in from userspace:
diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index 75fea0d48c0e..d360bf4d696b 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -139,7 +139,7 @@ void flush_thread(void)
flush_ptrace_hw_breakpoint(tsk);
memset(tsk->thread.tls_array, 0, sizeof(tsk->thread.tls_array));

- fpu__clear(&tsk->thread.fpu);
+ fpu__clear_all(&tsk->thread.fpu);
}

void disable_TSC(void)
diff --git a/arch/x86/kernel/signal.c b/arch/x86/kernel/signal.c
index 8eb7193e158d..ce9421ec285f 100644
--- a/arch/x86/kernel/signal.c
+++ b/arch/x86/kernel/signal.c
@@ -763,7 +763,7 @@ handle_signal(struct ksignal *ksig, struct pt_regs *regs)
/*
* Ensure the signal handler starts with the new fpu state.
*/
- fpu__clear(fpu);
+ fpu__clear_user_states(fpu);
}
signal_setup_done(failed, ksig, stepping);
}
--
2.17.1