x86/fpu: Make copy_xstate_to_kernel() usable for [x]fpregs_get()

When xsave with init state optimization is used then a component's state
in the task's xsave buffer can be stale when the corresponding feature bit
is not set.

fpregs_get() and xfpregs_get() invoke fpstate_sanitize_xstate() to update
the task's xsave buffer before retrieving the FX or FP state. That's just
duplicated code as copy_xstate_to_kernel() already handles this correctly.

Add a copy mode argument to the function which allows to restrict the state
copy to the FP and SSE features.

Also rename the function to copy_xstate_to_uabi_buf() so the name reflects
what it is doing.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20210623121452.805327286@linutronix.de

diff --git a/arch/x86/include/asm/fpu/xstate.h b/arch/x86/include/asm/fpu/xstate.h
index 1bb2d16..732ae79 100644 (file)
--- a/arch/x86/include/asm/fpu/xstate.h
+++ b/arch/x86/include/asm/fpu/xstate.h
@@ -103,12 +103,20 @@ extern void __init update_regset_xstate_info(unsigned int size,
 void *get_xsave_addr(struct xregs_state *xsave, int xfeature_nr);
 int using_compacted_format(void);
 int xfeature_size(int xfeature_nr);
-struct membuf;
-void copy_xstate_to_kernel(struct membuf to, struct xregs_state *xsave);
 int copy_kernel_to_xstate(struct xregs_state *xsave, const void *kbuf);
 int copy_user_to_xstate(struct xregs_state *xsave, const void __user *ubuf);
 void copy_supervisor_to_kernel(struct xregs_state *xsave);
 void copy_dynamic_supervisor_to_kernel(struct xregs_state *xstate, u64 mask);
 void copy_kernel_to_dynamic_supervisor(struct xregs_state *xstate, u64 mask);
 
+enum xstate_copy_mode {
+       XSTATE_COPY_FP,
+       XSTATE_COPY_FX,
+       XSTATE_COPY_XSAVE,
+};
+
+struct membuf;
+void copy_xstate_to_uabi_buf(struct membuf to, struct xregs_state *xsave,
+                            enum xstate_copy_mode mode);
+
 #endif

diff --git a/arch/x86/kernel/fpu/regset.c b/arch/x86/kernel/fpu/regset.c
index 7041b14..783f84d 100644 (file)
--- a/arch/x86/kernel/fpu/regset.c
+++ b/arch/x86/kernel/fpu/regset.c
@@ -93,7 +93,7 @@ int xstateregs_get(struct task_struct *target, const struct user_regset *regset,
 
        fpu__prepare_read(fpu);
 
-       copy_xstate_to_kernel(to, &fpu->state.xsave);
+       copy_xstate_to_uabi_buf(to, &fpu->state.xsave, XSTATE_COPY_XSAVE);
        return 0;
 }
 

diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c
index 4203247..8d023a2 100644 (file)
--- a/arch/x86/kernel/fpu/xstate.c
+++ b/arch/x86/kernel/fpu/xstate.c
@@ -1068,14 +1068,20 @@ static void copy_feature(bool from_xstate, struct membuf *to, void *xstate,
        membuf_write(to, from_xstate ? xstate : init_xstate, size);
 }
 
-/*
- * Convert from kernel XSAVE or XSAVES compacted format to UABI
- * non-compacted format and copy to a kernel-space ptrace buffer.
+/**
+ * copy_xstate_to_uabi_buf - Copy kernel saved xstate to a UABI buffer
+ * @to:                membuf descriptor
+ * @xsave:     The kernel xstate buffer to copy from
+ * @copy_mode: The requested copy mode
+ *
+ * Converts from kernel XSAVE or XSAVES compacted format to UABI conforming
+ * format, i.e. from the kernel internal hardware dependent storage format
+ * to the requested @mode. UABI XSTATE is always uncompacted!
  *
- * It supports partial copy but pos always starts from zero. This is called
- * from xstateregs_get() and there we check the CPU has XSAVE.
+ * It supports partial copy but @to.pos always starts from zero.
  */
-void copy_xstate_to_kernel(struct membuf to, struct xregs_state *xsave)
+void copy_xstate_to_uabi_buf(struct membuf to, struct xregs_state *xsave,
+                            enum xstate_copy_mode copy_mode)
 {
        const unsigned int off_mxcsr = offsetof(struct fxregs_state, mxcsr);
        struct xregs_state *xinit = &init_fpstate.xsave;
@@ -1083,12 +1089,22 @@ void copy_xstate_to_kernel(struct membuf to, struct xregs_state *xsave)
        unsigned int zerofrom;
        int i;
 
-       /*
-        * The destination is a ptrace buffer; we put in only user xstates:
-        */
-       memset(&header, 0, sizeof(header));
        header.xfeatures = xsave->header.xfeatures;
-       header.xfeatures &= xfeatures_mask_user();
+
+       /* Mask out the feature bits depending on copy mode */
+       switch (copy_mode) {
+       case XSTATE_COPY_FP:
+               header.xfeatures &= XFEATURE_MASK_FP;
+               break;
+
+       case XSTATE_COPY_FX:
+               header.xfeatures &= XFEATURE_MASK_FP | XFEATURE_MASK_SSE;
+               break;
+
+       case XSTATE_COPY_XSAVE:
+               header.xfeatures &= xfeatures_mask_user();
+               break;
+       }
 
        /* Copy FP state up to MXCSR */
        copy_feature(header.xfeatures & XFEATURE_MASK_FP, &to, &xsave->i387,
@@ -1109,6 +1125,9 @@ void copy_xstate_to_kernel(struct membuf to, struct xregs_state *xsave)
                     &to, &xsave->i387.xmm_space, &xinit->i387.xmm_space,
                     sizeof(xsave->i387.xmm_space));
 
+       if (copy_mode != XSTATE_COPY_XSAVE)
+               goto out;
+
        /* Zero the padding area */
        membuf_zero(&to, sizeof(xsave->i387.padding));
 
@@ -1150,6 +1169,7 @@ void copy_xstate_to_kernel(struct membuf to, struct xregs_state *xsave)
                zerofrom = xstate_offsets[i] + xstate_sizes[i];
        }
 
+out:
        if (to.left)
                membuf_zero(&to, to.left);
 }