[patch V2 14/52] x86/fpu: Make copy_xstate_to_kernel() usable for [x]fpregs_get()

Thomas Gleixner
2021-06-14T16:38:38Z

When xsave with init state optimiziation 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_uabi_xstate_to_membuf() so the name
reflects what it is doing.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
V2: New patch
---
arch/x86/include/asm/fpu/xstate.h | 12 +++++++++-
arch/x86/kernel/fpu/regset.c | 2 -
arch/x86/kernel/fpu/xstate.c | 42 ++++++++++++++++++++++++++++----------
3 files changed, 42 insertions(+), 14 deletions(-)

--- 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_
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_uabi_xstate_to_membuf(struct membuf to, struct xregs_state *xsave,
+ enum xstate_copy_mode mode);
+
#endif
--- a/arch/x86/kernel/fpu/regset.c
+++ b/arch/x86/kernel/fpu/regset.c
@@ -94,7 +94,7 @@ int xstateregs_get(struct task_struct *t

fpu__prepare_read(fpu);

- copy_xstate_to_kernel(to, &fpu->state.xsave);
+ copy_uabi_xstate_to_membuf(to, &fpu->state.xsave, XSTATE_COPY_XSAVE);
return 0;
}

--- a/arch/x86/kernel/fpu/xstate.c
+++ b/arch/x86/kernel/fpu/xstate.c
@@ -1062,14 +1062,20 @@ static void copy_feature(bool from_xstat
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_uabi_xstate_to_membuf - 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
*
- * It supports partial copy but pos always starts from zero. This is called
- * from xstateregs_get() and there we check the CPU has XSAVE.
+ * 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 @to.pos always starts from zero.
*/
-void copy_xstate_to_kernel(struct membuf to, struct xregs_state *xsave)
+void copy_uabi_xstate_to_membuf(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;
@@ -1077,12 +1083,22 @@ void copy_xstate_to_kernel(struct membuf
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,
@@ -1103,6 +1119,9 @@ void copy_xstate_to_kernel(struct membuf
&to, &xsave->i387.xmm_space, &xinit->i387.xmm_space,
16 * 16);

+ if (copy_mode != XSTATE_COPY_XSAVE)
+ goto out;
+
/* Zero the padding area */
membuf_zero(&to, sizeof(xsave->i387.padding));

@@ -1144,6 +1163,7 @@ void copy_xstate_to_kernel(struct membuf
zerofrom = xstate_offsets[i] + xstate_sizes[i];
}

+out:
if (to.left)
membuf_zero(&to, to.left);
}