x86/fpu/xstate: Define and use 'fpu_user_xstate_size'

The kernel xstate area can be in standard or compacted format;
it is always in standard format for user mode. When XSAVES is
enabled, the kernel uses the compacted format and it is necessary
to use a separate fpu_user_xstate_size for signal/ptrace frames.

Signed-off-by: Fenghua Yu <fenghua.yu@intel.com>
[ Rebased the patch and cleaned up the naming. ]
Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
Reviewed-by: Dave Hansen <dave.hansen@intel.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Quentin Casasnovas <quentin.casasnovas@oracle.com>
Cc: Ravi V. Shankar <ravi.v.shankar@intel.com>
Cc: Sai Praneeth Prakhya <sai.praneeth.prakhya@intel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/8756ec34dabddfc727cda5743195eb81e8caf91c.1463760376.git.yu-cheng.yu@intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

5 files changed, 73 insertions, 37 deletions

diff --git a/arch/x86/include/asm/fpu/xstate.h b/arch/x86/include/asm/fpu/xstate.h
index 38951b0fcc5a..16df2c44ac66 100644
--- a/arch/x86/include/asm/fpu/xstate.h
+++ b/arch/x86/include/asm/fpu/xstate.h
@@ -39,7 +39,6 @@
 #define REX_PREFIX
 #endif
 
-extern unsigned int xstate_size;
 extern u64 xfeatures_mask;
 extern u64 xstate_fx_sw_bytes[USER_XSTATE_FX_SW_WORDS];
 
diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index 62c6cc3cc5d3..0a16a16284f5 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -368,6 +368,7 @@ DECLARE_PER_CPU(struct irq_stack *, softirq_stack);
 #endif  /* X86_64 */
 
 extern unsigned int xstate_size;
+extern unsigned int fpu_user_xstate_size;
 
 struct perf_event;
 
diff --git a/arch/x86/kernel/fpu/init.c b/arch/x86/kernel/fpu/init.c
index aacfd7a82cec..5b1928c0aad4 100644
--- a/arch/x86/kernel/fpu/init.c
+++ b/arch/x86/kernel/fpu/init.c
@@ -195,7 +195,7 @@ static void __init fpu__init_task_struct_size(void)
 }
 
 /*
- * Set up the xstate_size based on the legacy FPU context size.
+ * Set up the user and kernel xstate_size based on the legacy FPU context size.
  *
  * We set this up first, and later it will be overwritten by
  * fpu__init_system_xstate() if the CPU knows about xstates.
@@ -226,6 +226,9 @@ static void __init fpu__init_system_xstate_size_legacy(void)
                 else
                         xstate_size = sizeof(struct fregs_state);
         }
+
+        fpu_user_xstate_size = xstate_size;
+
         /*
          * Quirk: we don't yet handle the XSAVES* instructions
          * correctly, as we don't correctly convert between
diff --git a/arch/x86/kernel/fpu/signal.c b/arch/x86/kernel/fpu/signal.c
index c6f2a3cee2c2..0d29d4de4209 100644
--- a/arch/x86/kernel/fpu/signal.c
+++ b/arch/x86/kernel/fpu/signal.c
@@ -32,7 +32,7 @@ static inline int check_for_xstate(struct fxregs_state __user *buf,
         /* Check for the first magic field and other error scenarios. */
         if (fx_sw->magic1 != FP_XSTATE_MAGIC1 ||
             fx_sw->xstate_size < min_xstate_size ||
-            fx_sw->xstate_size > xstate_size ||
+            fx_sw->xstate_size > fpu_user_xstate_size ||
             fx_sw->xstate_size > fx_sw->extended_size)
                 return -1;
 
@@ -89,7 +89,8 @@ static inline int save_xstate_epilog(void __user *buf, int ia32_frame)
         if (!use_xsave())
                 return err;
 
-        err |= __put_user(FP_XSTATE_MAGIC2, (__u32 *)(buf + xstate_size));
+        err |= __put_user(FP_XSTATE_MAGIC2,
+                          (__u32 *)(buf + fpu_user_xstate_size));
 
         /*
          * Read the xfeatures which we copied (directly from the cpu or
@@ -126,7 +127,7 @@ static inline int copy_fpregs_to_sigframe(struct xregs_state __user *buf)
         else
                 err = copy_fregs_to_user((struct fregs_state __user *) buf);
 
-        if (unlikely(err) && __clear_user(buf, xstate_size))
+        if (unlikely(err) && __clear_user(buf, fpu_user_xstate_size))
                 err = -EFAULT;
         return err;
 }
@@ -176,8 +177,19 @@ int copy_fpstate_to_sigframe(void __user *buf, void __user *buf_fx, int size)
                 if (ia32_fxstate)
                         copy_fxregs_to_kernel(&tsk->thread.fpu);
         } else {
+                /*
+                 * It is a *bug* if kernel uses compacted-format for xsave
+                 * area and we copy it out directly to a signal frame. It
+                 * should have been handled above by saving the registers
+                 * directly.
+                 */
+                if (boot_cpu_has(X86_FEATURE_XSAVES)) {
+                        WARN_ONCE(1, "x86/fpu: saving compacted-format xsave area to a signal frame!\n");
+                        return -1;
+                }
+
                 fpstate_sanitize_xstate(&tsk->thread.fpu);
-                if (__copy_to_user(buf_fx, xsave, xstate_size))
+                if (__copy_to_user(buf_fx, xsave, fpu_user_xstate_size))
                         return -1;
         }
 
@@ -344,7 +356,8 @@ static int __fpu__restore_sig(void __user *buf, void __user *buf_fx, int size)
 
 static inline int xstate_sigframe_size(void)
 {
-        return use_xsave() ? xstate_size + FP_XSTATE_MAGIC2_SIZE : xstate_size;
+        return use_xsave() ? fpu_user_xstate_size + FP_XSTATE_MAGIC2_SIZE :
+                        fpu_user_xstate_size;
 }
 
 /*
@@ -388,12 +401,12 @@ fpu__alloc_mathframe(unsigned long sp, int ia32_frame,
  */
 void fpu__init_prepare_fx_sw_frame(void)
 {
-        int size = xstate_size + FP_XSTATE_MAGIC2_SIZE;
+        int size = fpu_user_xstate_size + FP_XSTATE_MAGIC2_SIZE;
 
         fx_sw_reserved.magic1 = FP_XSTATE_MAGIC1;
         fx_sw_reserved.extended_size = size;
         fx_sw_reserved.xfeatures = xfeatures_mask;
-        fx_sw_reserved.xstate_size = xstate_size;
+        fx_sw_reserved.xstate_size = fpu_user_xstate_size;
 
         if (config_enabled(CONFIG_IA32_EMULATION) ||
             config_enabled(CONFIG_X86_32)) {
diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c
index 4ea2a59483c7..9c4da358ebb9 100644
--- a/arch/x86/kernel/fpu/xstate.c
+++ b/arch/x86/kernel/fpu/xstate.c
@@ -44,6 +44,13 @@ static unsigned int xstate_sizes[XFEATURE_MAX]   = { [ 0 ... XFEATURE_MAX - 1] =
 static unsigned int xstate_comp_offsets[sizeof(xfeatures_mask)*8];
 
 /*
+ * The XSAVE area of kernel can be in standard or compacted format;
+ * it is always in standard format for user mode. This is the user
+ * mode standard format size used for signal and ptrace frames.
+ */
+unsigned int fpu_user_xstate_size;
+
+/*
  * Clear all of the X86_FEATURE_* bits that are unavailable
  * when the CPU has no XSAVE support.
  */
@@ -171,7 +178,7 @@ void fpstate_sanitize_xstate(struct fpu *fpu)
          */
         while (xfeatures) {
                 if (xfeatures & 0x1) {
-                        int offset = xstate_offsets[feature_bit];
+                        int offset = xstate_comp_offsets[feature_bit];
                         int size = xstate_sizes[feature_bit];
 
                         memcpy((void *)fx + offset,
@@ -533,8 +540,9 @@ static void do_extra_xstate_size_checks(void)
         XSTATE_WARN_ON(paranoid_xstate_size != xstate_size);
 }
 
+
 /*
- * Calculate total size of enabled xstates in XCR0/xfeatures_mask.
+ * Get total size of enabled xstates in XCR0/xfeatures_mask.
  *
  * 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
@@ -544,34 +552,33 @@ static void do_extra_xstate_size_checks(void)
  * Note that we do not currently set any bits on IA32_XSS so
  * 'XCR0 | IA32_XSS == XCR0' for now.
  */
-static unsigned int __init calculate_xstate_size(void)
+static unsigned int __init get_xsaves_size(void)
 {
         unsigned int eax, ebx, ecx, edx;
-        unsigned int calculated_xstate_size;
+        /*
+         * - CPUID function 0DH, sub-function 1:
+         *    EBX enumerates the size (in bytes) required by
+         *    the XSAVES instruction for an XSAVE area
+         *    containing all the state components
+         *    corresponding to bits currently set in
+         *    XCR0 | IA32_XSS.
+         */
+        cpuid_count(XSTATE_CPUID, 1, &eax, &ebx, &ecx, &edx);
+        return ebx;
+}
 
-        if (!boot_cpu_has(X86_FEATURE_XSAVES)) {
-                /*
-                 * - CPUID function 0DH, sub-function 0:
-                 *    EBX enumerates the size (in bytes) required by
-                 *    the XSAVE instruction for an XSAVE area
-                 *    containing all the *user* state components
-                 *    corresponding to bits currently set in XCR0.
-                 */
-                cpuid_count(XSTATE_CPUID, 0, &eax, &ebx, &ecx, &edx);
-                calculated_xstate_size = ebx;
-        } else {
-                /*
-                 * - CPUID function 0DH, sub-function 1:
-                 *    EBX enumerates the size (in bytes) required by
-                 *    the XSAVES instruction for an XSAVE area
-                 *    containing all the state components
-                 *    corresponding to bits currently set in
-                 *    XCR0 | IA32_XSS.
-                 */
-                cpuid_count(XSTATE_CPUID, 1, &eax, &ebx, &ecx, &edx);
-                calculated_xstate_size = ebx;
-        }
-        return calculated_xstate_size;
+static unsigned int __init get_xsave_size(void)
+{
+        unsigned int eax, ebx, ecx, edx;
+        /*
+         * - CPUID function 0DH, sub-function 0:
+         *    EBX enumerates the size (in bytes) required by
+         *    the XSAVE instruction for an XSAVE area
+         *    containing all the *user* state components
+         *    corresponding to bits currently set in XCR0.
+         */
+        cpuid_count(XSTATE_CPUID, 0, &eax, &ebx, &ecx, &edx);
+        return ebx;
 }
 
 /*
@@ -591,7 +598,15 @@ static bool is_supported_xstate_size(unsigned int test_xstate_size)
 static int init_xstate_size(void)
 {
         /* Recompute the context size for enabled features: */
-        unsigned int possible_xstate_size = calculate_xstate_size();
+        unsigned int possible_xstate_size;
+        unsigned int xsave_size;
+
+        xsave_size = get_xsave_size();
+
+        if (boot_cpu_has(X86_FEATURE_XSAVES))
+                possible_xstate_size = get_xsaves_size();
+        else
+                possible_xstate_size = xsave_size;
 
         /* Ensure we have the space to store all enabled: */
         if (!is_supported_xstate_size(possible_xstate_size))
@@ -603,6 +618,11 @@ static int init_xstate_size(void)
          */
         xstate_size = possible_xstate_size;
         do_extra_xstate_size_checks();
+
+        /*
+         * User space is always in standard format.
+         */
+        fpu_user_xstate_size = xsave_size;
         return 0;
 }