[PATCH v4 07/10] x86/xsaves: Fix PTRACE frames for XSAVES

From: Yu-cheng Yu
Date: Fri Mar 04 2016 - 13:17:50 EST


XSAVES uses compacted format and is a kernel instruction. The kernel
should use standard-format, non-supervisor state data for PTRACE.

Signed-off-by: Yu-cheng Yu <yu-cheng.yu@xxxxxxxxx>
---
arch/x86/include/asm/fpu/xstate.h | 4 +
arch/x86/kernel/fpu/regset.c | 56 +++++++++---
arch/x86/kernel/fpu/xstate.c | 173 +++++++++++++++++++++++++++++++++++++-
3 files changed, 217 insertions(+), 16 deletions(-)

diff --git a/arch/x86/include/asm/fpu/xstate.h b/arch/x86/include/asm/fpu/xstate.h
index b4f5d94..a5cd808 100644
--- a/arch/x86/include/asm/fpu/xstate.h
+++ b/arch/x86/include/asm/fpu/xstate.h
@@ -50,5 +50,9 @@ extern void update_regset_xstate_info(unsigned int size, u64 xstate_mask);
void fpu__xstate_clear_all_cpu_caps(void);
void *get_xsave_addr(struct xregs_state *xsave, int xstate);
const void *get_xsave_field_ptr(int xstate_field);
+int copyout_from_xsaves(unsigned int pos, unsigned int count, void *kbuf,
+ void __user *ubuf, const struct xregs_state *xsave);
+int copyin_to_xsaves(const void *kbuf, const void __user *ubuf,
+ struct xregs_state *xsave);

#endif
diff --git a/arch/x86/kernel/fpu/regset.c b/arch/x86/kernel/fpu/regset.c
index 0bc3490..61fe8e9 100644
--- a/arch/x86/kernel/fpu/regset.c
+++ b/arch/x86/kernel/fpu/regset.c
@@ -4,6 +4,7 @@
#include <asm/fpu/internal.h>
#include <asm/fpu/signal.h>
#include <asm/fpu/regset.h>
+#include <asm/fpu/xstate.h>

/*
* The xstateregs_active() routine is the same as the regset_fpregs_active() routine,
@@ -82,21 +83,30 @@ int xstateregs_get(struct task_struct *target, const struct user_regset *regset,
if (!cpu_has_xsave)
return -ENODEV;

+ xsave = &fpu->state.xsave;
+
fpu__activate_fpstate_read(fpu);

- xsave = &fpu->state.xsave;
+ if (boot_cpu_has(X86_FEATURE_XSAVES)) {
+ ret = copyout_from_xsaves(pos, count, kbuf, ubuf, xsave);
+ } else {
+ fpstate_sanitize_xstate(fpu);
+
+ /*
+ * Copy the 48 bytes defined by the software into the xsave
+ * area in the thread struct, so that we can copy the whole
+ * area to user using one user_regset_copyout().
+ */
+ memcpy(&xsave->i387.sw_reserved,
+ xstate_fx_sw_bytes, sizeof(xstate_fx_sw_bytes));
+
+ /*
+ * Copy the xstate memory layout.
+ */
+ ret = user_regset_copyout(&pos,
+ &count, &kbuf, &ubuf, xsave, 0, -1);
+ }

- /*
- * Copy the 48bytes defined by the software first into the xstate
- * memory layout in the thread struct, so that we can copy the entire
- * xstateregs to the user using one user_regset_copyout().
- */
- memcpy(&xsave->i387.sw_reserved,
- xstate_fx_sw_bytes, sizeof(xstate_fx_sw_bytes));
- /*
- * Copy the xstate memory layout.
- */
- ret = user_regset_copyout(&pos, &count, &kbuf, &ubuf, xsave, 0, -1);
return ret;
}

@@ -111,11 +121,29 @@ int xstateregs_set(struct task_struct *target, const struct user_regset *regset,
if (!cpu_has_xsave)
return -ENODEV;

- fpu__activate_fpstate_write(fpu);
+ /*
+ * A whole standard-format XSAVE buffer is needed.
+ */
+ if ((pos != 0) || (count < user_xstate_size))
+ return -EFAULT;

xsave = &fpu->state.xsave;

- ret = user_regset_copyin(&pos, &count, &kbuf, &ubuf, xsave, 0, -1);
+ fpu__activate_fpstate_write(fpu);
+
+ if (boot_cpu_has(X86_FEATURE_XSAVES))
+ ret = copyin_to_xsaves(kbuf, ubuf, xsave);
+ else
+ ret = user_regset_copyin(&pos,
+ &count, &kbuf, &ubuf, xsave, 0, -1);
+
+ /*
+ * In case of failure, mark all states as init.
+ */
+
+ if (ret)
+ fpstate_init(&fpu->state);
+
/*
* mxcsr reserved bits must be masked to zero for security reasons.
*/
diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c
index aaab0d3..b9d4d59 100644
--- a/arch/x86/kernel/fpu/xstate.c
+++ b/arch/x86/kernel/fpu/xstate.c
@@ -677,7 +677,13 @@ void __init fpu__init_system_xstate(void)
return;
}

- update_regset_xstate_info(kernel_xstate_size, xfeatures_mask);
+ /*
+ * Update info used for ptrace frames; use standard-format size and no
+ * supervisor xstates.
+ */
+ update_regset_xstate_info(user_xstate_size,
+ xfeatures_mask & ~XFEATURE_MASK_SUPERVISOR);
+
fpu__init_prepare_fx_sw_frame();
setup_init_fpu_buf();
setup_xstate_comp();
@@ -701,6 +707,15 @@ void fpu__resume_cpu(void)
}

/*
+ * Get an xstate component address for either kernel or user mode.
+ */
+static void *get_xsave_addr_no_check(const struct xregs_state *xsave,
+ int feature_nr)
+{
+ return (void *)xsave + xstate_comp_offsets[feature_nr];
+}
+
+/*
* Given the xsave area and a state inside, this function returns the
* address of the state.
*
@@ -748,7 +763,7 @@ void *get_xsave_addr(struct xregs_state *xsave, int xstate_feature)
if (!(xsave->header.xfeatures & xstate_feature))
return NULL;

- return (void *)xsave + xstate_comp_offsets[feature_nr];
+ return get_xsave_addr_no_check(xsave, feature_nr);
}
EXPORT_SYMBOL_GPL(get_xsave_addr);

@@ -783,3 +798,157 @@ const void *get_xsave_field_ptr(int xsave_state)

return get_xsave_addr(&fpu->state.xsave, xsave_state);
}
+
+/*
+ * This is similar to user_regset_copyout(), but will not add offset to
+ * the source data pointer or increment pos, count, kbuf, and ubuf.
+ */
+static inline int xstate_copyout(unsigned int pos, unsigned int count,
+ void *kbuf, void __user *ubuf,
+ const void *data, const int start_pos,
+ const int end_pos)
+{
+ if ((count == 0) || (pos < start_pos))
+ return 0;
+
+ if (end_pos < 0 || pos < end_pos) {
+ unsigned int copy =
+ (end_pos < 0 ? count : min(count, end_pos - pos));
+
+ if (kbuf)
+ memcpy(kbuf + pos, data, copy);
+ else if (__copy_to_user(ubuf + pos, data, copy))
+ return -EFAULT;
+ }
+ return 0;
+}
+
+/*
+ * Convert from kernel XSAVES compacted format to standard format and copy
+ * to a ptrace buffer. It supports partial copy but pos always starts from
+ * zero. This is called from xstateregs_get() and there we check the cpu
+ * has XSAVES.
+ */
+int copyout_from_xsaves(unsigned int pos, unsigned int count, void *kbuf,
+ void __user *ubuf, const struct xregs_state *xsave)
+{
+ unsigned int offset, size;
+ int ret, i;
+ struct xstate_header header;
+
+ /*
+ * Currently copy_regset_to_user() starts from pos 0.
+ */
+ if (unlikely(pos != 0))
+ return -EFAULT;
+
+ /*
+ * The destination is a ptrace buffer; we put in only user xstates.
+ */
+ memset(&header, 0, sizeof(header));
+ header.xfeatures = xsave->header.xfeatures;
+ header.xfeatures &= ~XFEATURE_MASK_SUPERVISOR;
+
+ /*
+ * Copy xregs_state->header.
+ */
+ offset = offsetof(struct xregs_state, header);
+ size = sizeof(header);
+
+ ret = xstate_copyout(offset, size, kbuf, ubuf, &header, 0, count);
+
+ if (ret)
+ return ret;
+
+ for (i = 0; i < XFEATURE_MAX; i++) {
+ /*
+ * Copy only in-use xstates.
+ */
+ if (((header.xfeatures >> i) & 1) && xfeature_enabled(i)) {
+ void *src = get_xsave_addr_no_check(xsave, i);
+
+ offset = xstate_offsets[i];
+ size = xstate_sizes[i];
+
+ ret = xstate_copyout(offset, size, kbuf, ubuf, src, 0,
+ count);
+
+ if (ret)
+ return ret;
+
+ if (offset + size >= count)
+ break;
+ }
+ }
+
+ /*
+ * Fill xsave->i387.sw_reserved value for ptrace frame.
+ */
+ offset = offsetof(struct fxregs_state, sw_reserved);
+ size = sizeof(xstate_fx_sw_bytes);
+
+ ret = xstate_copyout(offset, size, kbuf, ubuf, xstate_fx_sw_bytes, 0,
+ count);
+
+ if (ret)
+ return ret;
+
+ return 0;
+}
+
+/*
+ * Convert from a ptrace standard-format buffer to kernel XSAVES format
+ * and copy to the target thread. This is called from xstateregs_set() and
+ * there we check the cpu has XSAVES and a whole standard-sized buffer
+ * exists.
+ */
+int copyin_to_xsaves(const void *kbuf, const void __user *ubuf,
+ struct xregs_state *xsave)
+{
+ unsigned int offset, size;
+ int i;
+ u64 xfeatures;
+
+ offset = offsetof(struct xregs_state, header);
+ size = sizeof(xfeatures);
+
+ if (kbuf)
+ memcpy(&xfeatures, kbuf + offset, size);
+ else if (__copy_from_user(&xfeatures, ubuf + offset, size))
+ return -EFAULT;
+
+ /*
+ * Reject if the user tries to set any supervisor xstates.
+ */
+ if (xfeatures & XFEATURE_MASK_SUPERVISOR)
+ return -EINVAL;
+
+ for (i = 0; i < XFEATURE_MAX; i++) {
+ u64 mask = ((u64)1 << i);
+
+ if ((xfeatures & mask) && xfeature_enabled(i)) {
+ void *dst = get_xsave_addr_no_check(xsave, i);
+
+ offset = xstate_offsets[i];
+ size = xstate_sizes[i];
+
+ if (kbuf)
+ memcpy(dst, kbuf + offset, size);
+ else if (__copy_from_user(dst, ubuf + offset, size))
+ return -EFAULT;
+ }
+ }
+
+ /*
+ * 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;
+
+ /*
+ * Add back in the features that came in from userspace.
+ */
+ xsave->header.xfeatures |= xfeatures;
+
+ return 0;
+}
--
1.9.1