[PATCH] x86/fpu/xstate: Return error if xfeature bit is unset in XSAVES compacted-format buffer

[Sai Praneeth Prakhya]

From: Sai Praneeth <sai.praneeth.prak...@intel.com>

Currently, XSAVES compacted-format buffer will always contain space for
all enabled states. If XSAVES compacted-format buffer is in use and
an xstate component (E.g: PKRU xstate) is not present in the buffer
(i.e. xcomp_bv does not have xfeature (E.g: XFEATURE_MASK_PKRU) bit
set), then fpu__xfeature_set_state() returns error.

Signed-off-by: Sai Praneeth Prakhya <sai.praneeth.prak...@intel.com>
Reported-by: Dave Hansen <dave.han...@intel.com>
Suggested-by: Dave Hansen <dave.han...@intel.com>
Cc: Dave Hansen <dave.han...@intel.com>
Cc: Yu-Cheng Yu <yu-cheng...@intel.com>
Cc: Fenghua Yu <fenghua...@intel.com>
Cc: Ravi Shankar <ravi.v.shan...@intel.com>
---
 arch/x86/kernel/fpu/xstate.c | 27 +++++++++++++++------------
 1 file changed, 15 insertions(+), 12 deletions(-)

diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c
index 680049aa4593..bc97aa2832c6 100644
--- a/arch/x86/kernel/fpu/xstate.c
+++ b/arch/x86/kernel/fpu/xstate.c
@@ -893,7 +893,7 @@ static void fpu__xfeature_set_non_init(struct xregs_state 
*xsave,
  *     address of the state in the xsave area or NULL if the state
  *     is not present or is in its 'init state'.
  */
-static void fpu__xfeature_set_state(int xstate_feature_mask,
+static int fpu__xfeature_set_state(int xstate_feature_mask,
                void *xstate_feature_src, size_t len)
 {
        struct xregs_state *xsave = &current->thread.fpu.state.xsave;
@@ -902,7 +902,7 @@ static void fpu__xfeature_set_state(int xstate_feature_mask,
 
        if (!boot_cpu_has(X86_FEATURE_XSAVE)) {
                WARN_ONCE(1, "%s() attempted with no xsave support", __func__);
-               return;
+               return -ENXIO;
        }
 
        /*
@@ -913,14 +913,16 @@ static void fpu__xfeature_set_state(int 
xstate_feature_mask,
        fpu__current_fpstate_write_begin();
 
        /*
-        * This method *WILL* *NOT* work for compact-format
-        * buffers.  If the 'xstate_feature_mask' is unset in
-        * xcomp_bv then we may need to move other feature state
-        * "up" in the buffer.
+        * This method will not work on XSAVES compacted-format buffer
+        * that do not have space allocated for the state we are trying
+        * to set. Currently, the kernel always allocates space for all
+        * enabled states. This check makes sure that holds true.
         */
-       if (xsave->header.xcomp_bv & xstate_feature_mask) {
+       if (!(xsave->header.xcomp_bv & xstate_feature_mask) &&\
+               using_compacted_format()) {
                WARN_ON_ONCE(1);
-               goto out;
+               fpu__current_fpstate_write_end();
+               return -EINVAL;
        }
 
        /* find the location in the xsave buffer of the desired state */
@@ -940,12 +942,14 @@ static void fpu__xfeature_set_state(int 
xstate_feature_mask,
         * in the buffer now.
         */
        fpu__xfeature_set_non_init(xsave, xstate_feature_mask);
-out:
+
        /*
         * We are done writing to the 'fpu'.  Reenable preeption
         * and (possibly) move the fpstate back in to the fpregs.
         */
        fpu__current_fpstate_write_end();
+
+       return 0;
 }
 
 #define NR_VALID_PKRU_BITS (CONFIG_NR_PROTECTION_KEYS * 2)
@@ -1014,9 +1018,8 @@ int arch_set_user_pkey_access(struct task_struct *tsk, 
int pkey,
         */
        new_pkru_state.pad = 0;
 
-       fpu__xfeature_set_state(XFEATURE_MASK_PKRU, &new_pkru_state, 
sizeof(new_pkru_state));
-
-       return 0;
+       return fpu__xfeature_set_state(XFEATURE_MASK_PKRU, &new_pkru_state,
+                       sizeof(new_pkru_state));
 }
 
 /*
-- 
2.1.4