[RFC PATCH v6 04/26] x86/fpu/xstate: Introduce XSAVES system states

Yu-cheng Yu
2018-11-20T08:19:56Z

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 | 3 +-
arch/x86/include/asm/fpu/xstate.h | 4 +-
arch/x86/kernel/fpu/core.c | 6 +-
arch/x86/kernel/fpu/init.c | 10 ---
arch/x86/kernel/fpu/xstate.c | 94 +++++++++++++++++++----------
5 files changed, 69 insertions(+), 48 deletions(-)

diff --git a/arch/x86/include/asm/fpu/internal.h b/arch/x86/include/asm/fpu/internal.h
index 540ef09d4b6e..3f38c9aec553 100644
--- a/arch/x86/include/asm/fpu/internal.h
+++ b/arch/x86/include/asm/fpu/internal.h
@@ -45,7 +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:
@@ -93,7 +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)
diff --git a/arch/x86/include/asm/fpu/xstate.h b/arch/x86/include/asm/fpu/xstate.h
index 76f83d2ac10e..d8e2ec99f635 100644
--- a/arch/x86/include/asm/fpu/xstate.h
+++ b/arch/x86/include/asm/fpu/xstate.h
@@ -19,9 +19,6 @@
#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 | \
@@ -40,6 +37,7 @@
#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 4bd56079048f..5f076f593fa9 100644
--- a/arch/x86/kernel/fpu/core.c
+++ b/arch/x86/kernel/fpu/core.c
@@ -365,8 +365,12 @@ void fpu__drop(struct fpu *fpu)
*/
static inline void copy_init_user_fpstate_to_fpregs(void)
{
+ /*
+ * 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, xfeatures_mask_user);
else if (static_cpu_has(X86_FEATURE_FXSR))
copy_kernel_to_fxregs(&init_fpstate.fxsave);
else
diff --git a/arch/x86/kernel/fpu/init.c b/arch/x86/kernel/fpu/init.c
index 761c3a5a9e07..eaf9d9d479a5 100644
--- a/arch/x86/kernel/fpu/init.c
+++ b/arch/x86/kernel/fpu/init.c
@@ -222,16 +222,6 @@ 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/xstate.c b/arch/x86/kernel/fpu/xstate.c
index 326b64a61fc9..f6d2e2e53463 100644
--- a/arch/x86/kernel/fpu/xstate.c
+++ b/arch/x86/kernel/fpu/xstate.c
@@ -58,9 +58,19 @@ 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;
@@ -85,7 +95,7 @@ void fpu__xstate_clear_all_cpu_caps(void)
*/
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;
@@ -164,7 +174,7 @@ 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;

/*
@@ -219,28 +229,27 @@ 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));
}

/*
@@ -346,7 +355,7 @@ 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;

/*
@@ -419,7 +428,7 @@ 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
@@ -442,7 +451,7 @@ static int xfeature_uncompacted_offset(int xfeature_nr)
* format. Checking a system state's uncompacted offset is
* an error.
*/
- if (XFEATURE_MASK_SUPERVISOR & (1 << xfeature_nr)) {
+ if (~xfeatures_mask_user & BIT_ULL(xfeature_nr)) {
WARN_ONCE(1, "No fixed offset for xstate %d\n", xfeature_nr);
return -1;
}
@@ -614,15 +623,12 @@ 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)
{
@@ -704,6 +710,7 @@ static int 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);
fpu__xstate_clear_all_cpu_caps();
@@ -717,6 +724,8 @@ void __init fpu__init_system_xstate(void)
{
unsigned int eax, ebx, ecx, edx;
static int on_boot_cpu __initdata = 1;
+ u64 cpu_system_xfeatures_mask;
+ u64 cpu_user_xfeatures_mask;
int err;
int i;

@@ -739,10 +748,23 @@ 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);
+ cpu_user_xfeatures_mask = 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);
+ cpu_system_xfeatures_mask = ecx + ((u64)edx << 32);
+
+ xfeatures_mask_all = cpu_user_xfeatures_mask | cpu_system_xfeatures_mask;
+
+ 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
@@ -757,10 +779,12 @@ 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 & cpu_user_xfeatures_mask;
+ xfeatures_mask_system = xfeatures_mask_all & cpu_system_xfeatures_mask;

/* Enable xstate instructions to be able to continue with initialization: */
fpu__init_cpu_xstate();
@@ -772,7 +796,7 @@ 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();
@@ -780,7 +804,7 @@ 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;
@@ -800,6 +824,12 @@ 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);
}

/*
@@ -849,9 +879,9 @@ void *get_xsave_addr(struct xregs_state *xsave, int xstate_feature)
/*
* 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 & xstate_feature),
+ WARN_ONCE(!(xfeatures_mask_all & xstate_feature),
"get of unsupported state");
/*
* This assumes the last 'xsave*' instruction to
@@ -1001,7 +1031,7 @@ 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:
@@ -1085,7 +1115,7 @@ 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:
@@ -1178,7 +1208,7 @@ 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_all & ~xfeatures_mask_user);

/*
* Add back in the features that came in from userspace:
@@ -1234,7 +1264,7 @@ 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_all & ~xfeatures_mask_user);

/*
* Add back in the features that came in from userspace:
--
2.17.1