x86, xsave: Sync xsave memory layout with its header for user handling

With xsaveopt, if a processor implementation discern that a processor state
component is in its initialized state it may modify the corresponding bit in
the xsave_hdr.xstate_bv as '0', with out modifying the corresponding memory
layout. Hence wHile presenting the xstate information to the user, we always
ensure that the memory layout of a feature will be in the init state if the
corresponding header bit is zero. This ensures the consistency and avoids the
condition of the user seeing some some stale state in the memory layout during
signal handling, debugging etc.

Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>
LKML-Reference: <20100719230205.351459480@sbs-t61.sc.intel.com>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>

1 files changed, 88 insertions, 1 deletions

diff --git a/arch/x86/kernel/xsave.c b/arch/x86/kernel/xsave.c
index 4993caa4181c..368047c8d507 100644
--- a/arch/x86/kernel/xsave.c
+++ b/arch/x86/kernel/xsave.c
@@ -24,6 +24,76 @@ struct _fpx_sw_bytes fx_sw_reserved_ia32;
 static unsigned int *xstate_offsets, *xstate_sizes, xstate_features;
 
 /*
+ * If a processor implementation discern that a processor state component is
+ * in its initialized state it may modify the corresponding bit in the
+ * xsave_hdr.xstate_bv as '0', with out modifying the corresponding memory
+ * layout in the case of xsaveopt. While presenting the xstate information to
+ * the user, we always ensure that the memory layout of a feature will be in
+ * the init state if the corresponding header bit is zero. This is to ensure
+ * that the user doesn't see some stale state in the memory layout during
+ * signal handling, debugging etc.
+ */
+void __sanitize_i387_state(struct task_struct *tsk)
+{
+        u64 xstate_bv;
+        int feature_bit = 0x2;
+        struct i387_fxsave_struct *fx = &tsk->thread.fpu.state->fxsave;
+
+        if (!fx)
+                return;
+
+        BUG_ON(task_thread_info(tsk)->status & TS_USEDFPU);
+
+        xstate_bv = tsk->thread.fpu.state->xsave.xsave_hdr.xstate_bv;
+
+        /*
+         * None of the feature bits are in init state. So nothing else
+         * to do for us, as the memory layout is upto date.
+         */
+        if ((xstate_bv & pcntxt_mask) == pcntxt_mask)
+                return;
+
+        /*
+         * FP is in init state
+         */
+        if (!(xstate_bv & XSTATE_FP)) {
+                fx->cwd = 0x37f;
+                fx->swd = 0;
+                fx->twd = 0;
+                fx->fop = 0;
+                fx->rip = 0;
+                fx->rdp = 0;
+                memset(&fx->st_space[0], 0, 128);
+        }
+
+        /*
+         * SSE is in init state
+         */
+        if (!(xstate_bv & XSTATE_SSE))
+                memset(&fx->xmm_space[0], 0, 256);
+
+        xstate_bv = (pcntxt_mask & ~xstate_bv) >> 2;
+
+        /*
+         * Update all the other memory layouts for which the corresponding
+         * header bit is in the init state.
+         */
+        while (xstate_bv) {
+                if (xstate_bv & 0x1) {
+                        int offset = xstate_offsets[feature_bit];
+                        int size = xstate_sizes[feature_bit];
+
+                        memcpy(((void *) fx) + offset,
+                               ((void *) init_xstate_buf) + offset,
+                               size);
+                }
+
+                xstate_bv >>= 1;
+                feature_bit++;
+        }
+}
+
+/*
  * Check for the presence of extended state information in the
  * user fpstate pointer in the sigcontext.
  */
@@ -112,6 +182,7 @@ int save_i387_xstate(void __user *buf)
                 task_thread_info(tsk)->status &= ~TS_USEDFPU;
                 stts();
         } else {
+                sanitize_i387_state(tsk);
                 if (__copy_to_user(buf, &tsk->thread.fpu.state->fxsave,
                                    xstate_size))
                         return -1;
@@ -333,10 +404,26 @@ static void setup_xstate_features(void)
  */
 static void __init setup_xstate_init(void)
 {
+        setup_xstate_features();
+
+        /*
+         * Setup init_xstate_buf to represent the init state of
+         * all the features managed by the xsave
+         */
         init_xstate_buf = alloc_bootmem(xstate_size);
         init_xstate_buf->i387.mxcsr = MXCSR_DEFAULT;
 
-        setup_xstate_features();
+        clts();
+        /*
+         * Init all the features state with header_bv being 0x0
+         */
+        xrstor_state(init_xstate_buf, -1);
+        /*
+         * Dump the init state again. This is to identify the init state
+         * of any feature which is not represented by all zero's.
+         */
+        xsave_state(init_xstate_buf, -1);
+        stts();
 }
 
 /*