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[PATCH 21/33] x86/fpu: Add FPU state copying quirk to handle XRSTOR failure on Intel Skylake CPUs

From Ingo Molnar <mingo@kernel.org>
Newsgroups linux.kernel
Subject [PATCH 21/33] x86/fpu: Add FPU state copying quirk to handle XRSTOR failure on Intel Skylake CPUs
Date 2017-09-23 15:10 +0200
Message-ID <usSlX-3wU-9@gated-at.bofh.it> (permalink)
References <usSlX-3wU-3@gated-at.bofh.it>
Organization linux.* mail to news gateway

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From: Rik van Riel <riel@redhat.com>

On Skylake CPUs I noticed that XRSTOR is unable to deal with states
created by copyout_from_xsaves() if the xstate has only SSE/YMM state, and
no FP state. That is, xfeatures had XFEATURE_MASK_SSE set, but not
XFEATURE_MASK_FP.

The reason is that part of the SSE/YMM state lives in the MXCSR and
MXCSR_FLAGS fields of the FP state.

Ensure that whenever we copy SSE or YMM state around, the MXCSR and
MXCSR_FLAGS fields are also copied around.

Signed-off-by: Rik van Riel <riel@redhat.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Borislav Petkov <bp@suse.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Yu-cheng Yu <yu-cheng.yu@intel.com>
Link: http://lkml.kernel.org/r/20170210085445.0f1cc708@annuminas.surriel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 arch/x86/include/asm/fpu/types.h |  3 +++
 arch/x86/kernel/fpu/xstate.c     | 42 ++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 45 insertions(+)

diff --git a/arch/x86/include/asm/fpu/types.h b/arch/x86/include/asm/fpu/types.h
index 0c314a397cf5..71db45ca8870 100644
--- a/arch/x86/include/asm/fpu/types.h
+++ b/arch/x86/include/asm/fpu/types.h
@@ -68,6 +68,9 @@ struct fxregs_state {
 /* Default value for fxregs_state.mxcsr: */
 #define MXCSR_DEFAULT		0x1f80
 
+/* Copy both mxcsr & mxcsr_flags with a single u64 memcpy: */
+#define MXCSR_AND_FLAGS_SIZE sizeof(u64)
+
 /*
  * Software based FPU emulation state. This is arbitrary really,
  * it matches the x87 format to make it easier to understand:
diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c
index 0ef35040d0ad..41c52256bdce 100644
--- a/arch/x86/kernel/fpu/xstate.c
+++ b/arch/x86/kernel/fpu/xstate.c
@@ -921,6 +921,23 @@ int arch_set_user_pkey_access(struct task_struct *tsk, int pkey,
 #endif /* ! CONFIG_ARCH_HAS_PKEYS */
 
 /*
+ * Weird legacy quirk: SSE and YMM states store information in the
+ * MXCSR and MXCSR_FLAGS fields of the FP area. That means if the FP
+ * area is marked as unused in the xfeatures header, we need to copy
+ * MXCSR and MXCSR_FLAGS if either SSE or YMM are in use.
+ */
+static inline bool xfeatures_mxcsr_quirk(u64 xfeatures)
+{
+	if (!(xfeatures & (XFEATURE_MASK_SSE|XFEATURE_MASK_YMM)))
+		return 0;
+
+	if (xfeatures & XFEATURE_MASK_FP)
+		return 0;
+
+	return 1;
+}
+
+/*
  * This is similar to user_regset_copyout(), but will not add offset to
  * the source data pointer or increment pos, count, kbuf, and ubuf.
  */
@@ -988,6 +1005,12 @@ int copy_xstate_to_kernel(void *kbuf, struct xregs_state *xsave, unsigned int of
 
 	}
 
+	if (xfeatures_mxcsr_quirk(header.xfeatures)) {
+		offset = offsetof(struct fxregs_state, mxcsr);
+		size = MXCSR_AND_FLAGS_SIZE;
+		__copy_xstate_to_kernel(kbuf, &xsave->i387.mxcsr, offset, size, size_total);
+	}
+
 	/*
 	 * Fill xsave->i387.sw_reserved value for ptrace frame:
 	 */
@@ -1070,6 +1093,12 @@ int copy_xstate_to_user(void __user *ubuf, struct xregs_state *xsave, unsigned i
 
 	}
 
+	if (xfeatures_mxcsr_quirk(header.xfeatures)) {
+		offset = offsetof(struct fxregs_state, mxcsr);
+		size = MXCSR_AND_FLAGS_SIZE;
+		__copy_xstate_to_user(ubuf, &xsave->i387.mxcsr, offset, size, size_total);
+	}
+
 	/*
 	 * Fill xsave->i387.sw_reserved value for ptrace frame:
 	 */
@@ -1122,6 +1151,12 @@ int copy_kernel_to_xstate(struct xregs_state *xsave, const void *kbuf)
 		}
 	}
 
+	if (xfeatures_mxcsr_quirk(xfeatures)) {
+		offset = offsetof(struct fxregs_state, mxcsr);
+		size = MXCSR_AND_FLAGS_SIZE;
+		memcpy(&xsave->i387.mxcsr, kbuf + offset, size);
+	}
+
 	/*
 	 * The state that came in from userspace was user-state only.
 	 * Mask all the user states out of 'xfeatures':
@@ -1177,6 +1212,13 @@ int copy_user_to_xstate(struct xregs_state *xsave, const void __user *ubuf)
 		}
 	}
 
+	if (xfeatures_mxcsr_quirk(xfeatures)) {
+		offset = offsetof(struct fxregs_state, mxcsr);
+		size = MXCSR_AND_FLAGS_SIZE;
+		if (__copy_from_user(&xsave->i387.mxcsr, ubuf + offset, size))
+			return -EFAULT;
+	}
+
 	/*
 	 * The state that came in from userspace was user-state only.
 	 * Mask all the user states out of 'xfeatures':
-- 
2.11.0

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[PATCH 00/33] x86 FPU fixes and cleanups for v4.14 Ingo Molnar <mingo@kernel.org> - 2017-09-23 15:10 +0200
  [PATCH 19/33] x86/fpu: Decouple fpregs_activate()/fpregs_deactivate() from fpu->fpregs_active Ingo Molnar <mingo@kernel.org> - 2017-09-23 15:10 +0200
    [tip:x86/fpu] x86/fpu: Decouple  fpregs_activate()/fpregs_deactivate() from fpu->fpregs_active tip-bot for Ingo Molnar <tipbot@zytor.com> - 2017-09-26 10:40 +0200
  [PATCH 15/33] x86/fpu: Simplify fpu->fpregs_active use Ingo Molnar <mingo@kernel.org> - 2017-09-23 15:10 +0200
    [tip:x86/fpu] x86/fpu: Simplify fpu->fpregs_active use tip-bot for Ingo Molnar <tipbot@zytor.com> - 2017-09-26 10:40 +0200
  [PATCH 26/33] x86/fpu: Reinitialize FPU registers if restoring FPU state fails Ingo Molnar <mingo@kernel.org> - 2017-09-23 15:10 +0200
    [tip:x86/fpu] x86/fpu: Reinitialize FPU registers if restoring FPU  state fails tip-bot for Eric Biggers <tipbot@zytor.com> - 2017-09-26 10:40 +0200
  [PATCH 32/33] x86/fpu: Rename fpu__activate_curr() to fpu__initialize() Ingo Molnar <mingo@kernel.org> - 2017-09-23 15:10 +0200
    [tip:x86/fpu] x86/fpu: Rename fpu__activate_curr() to  fpu__initialize() tip-bot for Ingo Molnar <tipbot@zytor.com> - 2017-09-26 10:50 +0200
  [PATCH 31/33] x86/fpu: Simplify and speed up fpu__copy() Ingo Molnar <mingo@kernel.org> - 2017-09-23 15:10 +0200
    [tip:x86/fpu] x86/fpu: Simplify and speed up fpu__copy() tip-bot for Ingo Molnar <tipbot@zytor.com> - 2017-09-26 10:50 +0200
  [PATCH 21/33] x86/fpu: Add FPU state copying quirk to handle XRSTOR failure on Intel Skylake CPUs Ingo Molnar <mingo@kernel.org> - 2017-09-23 15:10 +0200
    [tip:x86/fpu] x86/fpu: Add FPU state copying quirk to handle XRSTOR  failure on Intel Skylake CPUs tip-bot for Rik van Riel <tipbot@zytor.com> - 2017-09-26 10:40 +0200
  [PATCH 13/33] x86/fpu: Remove 'kbuf' parameter from the copy_user_to_xstate() API Ingo Molnar <mingo@kernel.org> - 2017-09-23 15:10 +0200
    [tip:x86/fpu] x86/fpu: Remove 'kbuf' parameter from the  copy_user_to_xstate() API tip-bot for Ingo Molnar <tipbot@zytor.com> - 2017-09-26 10:40 +0200
  [PATCH 33/33] x86/fpu: Rename fpu__activate_fpstate_read/write() to fpu__read/write() Ingo Molnar <mingo@kernel.org> - 2017-09-23 15:10 +0200
  [PATCH 02/33] x86/fpu: Split copy_xstate_to_user() into copy_xstate_to_kernel() & copy_xstate_to_user() Ingo Molnar <mingo@kernel.org> - 2017-09-23 15:10 +0200
    [tip:x86/fpu] x86/fpu: Split copy_xstate_to_user() into  copy_xstate_to_kernel() & copy_xstate_to_user() tip-bot for Ingo Molnar <tipbot@zytor.com> - 2017-09-26 10:30 +0200
  [PATCH 16/33] x86/fpu: Make the fpu state change in fpu__clear() scheduler-atomic Ingo Molnar <mingo@kernel.org> - 2017-09-23 15:10 +0200
    [tip:x86/fpu] x86/fpu: Make the fpu state change in fpu__clear()  scheduler-atomic tip-bot for Ingo Molnar <tipbot@zytor.com> - 2017-09-26 10:40 +0200
  [PATCH 14/33] x86/fpu: Flip the parameter order in copy_*_to_xstate() Ingo Molnar <mingo@kernel.org> - 2017-09-23 15:10 +0200
    [tip:x86/fpu] x86/fpu: Flip the parameter order in  copy_*_to_xstate() tip-bot for Ingo Molnar <tipbot@zytor.com> - 2017-09-26 10:40 +0200
  [PATCH 11/33] x86/fpu: Split copy_user_to_xstate() into copy_kernel_to_xstate() & copy_user_to_xstate() Ingo Molnar <mingo@kernel.org> - 2017-09-23 15:10 +0200
    [tip:x86/fpu] x86/fpu: Split copy_user_to_xstate() into  copy_kernel_to_xstate() & copy_user_to_xstate() tip-bot for Ingo Molnar <tipbot@zytor.com> - 2017-09-26 10:40 +0200
  [PATCH 07/33] x86/fpu: Remove the 'start_pos' parameter from the __copy_xstate_to_*() functions Ingo Molnar <mingo@kernel.org> - 2017-09-23 15:10 +0200
    [tip:x86/fpu] x86/fpu: Remove the 'start_pos' parameter from the  __copy_xstate_to_*() functions tip-bot for Ingo Molnar <tipbot@zytor.com> - 2017-09-26 10:40 +0200
  [PATCH 01/33] x86/fpu: Rename copyin_to_xsaves()/copyout_from_xsaves() to copy_user_to_xstate()/copy_xstate_to_user() Ingo Molnar <mingo@kernel.org> - 2017-09-23 15:10 +0200
    [tip:x86/fpu] x86/fpu: Rename  copyin_to_xsaves()/copyout_from_xsaves() to  copy_user_to_xstate()/copy_xstate_to_user() tip-bot for Ingo Molnar <tipbot@zytor.com> - 2017-09-26 10:30 +0200
  [PATCH 29/33] x86/fpu: Rename fpu::fpstate_active to fpu::initialized Ingo Molnar <mingo@kernel.org> - 2017-09-23 15:10 +0200
    [tip:x86/fpu] x86/fpu: Rename fpu::fpstate_active to  fpu::initialized tip-bot for Ingo Molnar <tipbot@zytor.com> - 2017-09-26 10:50 +0200
  [PATCH 17/33] x86/fpu: Split the state handling in fpu__drop() Ingo Molnar <mingo@kernel.org> - 2017-09-23 15:10 +0200
    [tip:x86/fpu] x86/fpu: Split the state handling in fpu__drop() tip-bot for Ingo Molnar <tipbot@zytor.com> - 2017-09-26 10:40 +0200
  [PATCH 09/33] x86/fpu: Change 'size_total' parameter to unsigned and standardize the size checks in copy_xstate_to_*() Ingo Molnar <mingo@kernel.org> - 2017-09-23 15:10 +0200
    [tip:x86/fpu] x86/fpu: Change 'size_total' parameter to unsigned  and standardize the size checks in copy_xstate_to_*() tip-bot for Ingo Molnar <tipbot@zytor.com> - 2017-09-26 10:40 +0200
  [PATCH 30/33] x86/fpu: Fix stale comments about lazy FPU logic Ingo Molnar <mingo@kernel.org> - 2017-09-23 15:10 +0200
    [tip:x86/fpu] x86/fpu: Fix stale comments about lazy FPU logic tip-bot for Ingo Molnar <tipbot@zytor.com> - 2017-09-26 10:50 +0200
  [PATCH 08/33] x86/fpu: Clarify parameter names in the copy_xstate_to_*() methods Ingo Molnar <mingo@kernel.org> - 2017-09-23 15:10 +0200
    Re: [PATCH 08/33] x86/fpu: Clarify parameter names in the  copy_xstate_to_*() methods Thomas Gleixner <tglx@linutronix.de> - 2017-09-25 22:00 +0200
      Re: [PATCH 08/33] x86/fpu: Clarify parameter names in the  copy_xstate_to_*() methods Thomas Gleixner <tglx@linutronix.de> - 2017-09-25 22:10 +0200
    [tip:x86/fpu] x86/fpu: Clarify parameter names in the  copy_xstate_to_*() methods tip-bot for Ingo Molnar <tipbot@zytor.com> - 2017-09-26 10:40 +0200
  [PATCH 20/33] x86/fpu: Remove struct fpu::fpregs_active Ingo Molnar <mingo@kernel.org> - 2017-09-23 15:10 +0200
    [tip:x86/fpu] x86/fpu: Remove struct fpu::fpregs_active tip-bot for Ingo Molnar <tipbot@zytor.com> - 2017-09-26 10:40 +0200
  [PATCH 03/33] x86/fpu: Remove 'ubuf' parameter from the copy_xstate_to_kernel() APIs Ingo Molnar <mingo@kernel.org> - 2017-09-23 15:10 +0200
    [tip:x86/fpu] x86/fpu: Remove 'ubuf' parameter from the  copy_xstate_to_kernel() APIs tip-bot for Ingo Molnar <tipbot@zytor.com> - 2017-09-26 10:30 +0200
  [PATCH 23/33] x86/fpu: Turn WARN_ON() in context switch into WARN_ON_FPU() Ingo Molnar <mingo@kernel.org> - 2017-09-23 15:10 +0200
    [tip:x86/fpu] x86/fpu: Turn WARN_ON() in context switch into  WARN_ON_FPU() tip-bot for Andi Kleen <tipbot@zytor.com> - 2017-09-26 10:40 +0200
  [PATCH 22/33] x86/fpu: Fix boolreturn.cocci warnings Ingo Molnar <mingo@kernel.org> - 2017-09-23 15:10 +0200
    [tip:x86/fpu] x86/fpu: Fix boolreturn.cocci warnings tip-bot for kbuild test robot <tipbot@zytor.com> - 2017-09-26 10:40 +0200
  [PATCH 06/33] x86/fpu: Clean up the parameter definitions of copy_xstate_to_*() Ingo Molnar <mingo@kernel.org> - 2017-09-23 15:10 +0200
    [tip:x86/fpu] x86/fpu: Clean up the parameter definitions of  copy_xstate_to_*() tip-bot for Ingo Molnar <tipbot@zytor.com> - 2017-09-26 10:40 +0200
  [PATCH 04/33] x86/fpu: Remove 'kbuf' parameter from the copy_xstate_to_user() APIs Ingo Molnar <mingo@kernel.org> - 2017-09-23 15:10 +0200
    [tip:x86/fpu] x86/fpu: Remove 'kbuf' parameter from the  copy_xstate_to_user() APIs tip-bot for Ingo Molnar <tipbot@zytor.com> - 2017-09-26 10:40 +0200
  [PATCH 05/33] x86/fpu: Clean up parameter order in the copy_xstate_to_*() APIs Ingo Molnar <mingo@kernel.org> - 2017-09-23 15:10 +0200
    [tip:x86/fpu] x86/fpu: Clean up parameter order in the  copy_xstate_to_*() APIs tip-bot for Ingo Molnar <tipbot@zytor.com> - 2017-09-26 10:40 +0200
  [PATCH 24/33] x86/fpu: Don't let userspace set bogus xcomp_bv Ingo Molnar <mingo@kernel.org> - 2017-09-23 15:10 +0200
    [tip:x86/fpu] x86/fpu: Don't let userspace set bogus xcomp_bv tip-bot for Eric Biggers <tipbot@zytor.com> - 2017-09-26 10:50 +0200
  [PATCH 18/33] x86/fpu: Change fpu->fpregs_active users to fpu->fpstate_active Ingo Molnar <mingo@kernel.org> - 2017-09-23 15:10 +0200
    [tip:x86/fpu] x86/fpu: Change fpu->fpregs_active users to  fpu->fpstate_active tip-bot for Ingo Molnar <tipbot@zytor.com> - 2017-09-26 10:40 +0200
  [PATCH 27/33] x86/fpu: Simplify fpu__activate_fpstate_read() Ingo Molnar <mingo@kernel.org> - 2017-09-23 15:10 +0200
    [tip:x86/fpu] x86/fpu: Fix fpu__activate_fpstate_read() and update  comments tip-bot for Ingo Molnar <tipbot@zytor.com> - 2017-09-26 10:40 +0200
  [PATCH 12/33] x86/fpu: Remove 'ubuf' parameter from the copy_kernel_to_xstate() API Ingo Molnar <mingo@kernel.org> - 2017-09-23 15:10 +0200
    [tip:x86/fpu] x86/fpu: Remove 'ubuf' parameter from the  copy_kernel_to_xstate() API tip-bot for Ingo Molnar <tipbot@zytor.com> - 2017-09-26 10:40 +0200
  [PATCH 25/33] x86/fpu: Tighten validation of user-supplied xstate_header Ingo Molnar <mingo@kernel.org> - 2017-09-23 15:10 +0200
  [PATCH 28/33] x86/fpu: Remove fpu__current_fpstate_write_begin/end() Ingo Molnar <mingo@kernel.org> - 2017-09-23 15:10 +0200
    [tip:x86/fpu] x86/fpu: Remove  fpu__current_fpstate_write_begin/end() tip-bot for Ingo Molnar <tipbot@zytor.com> - 2017-09-26 10:40 +0200
  Re: [PATCH 00/33] x86 FPU fixes and cleanups for v4.14 Ingo Molnar <mingo@kernel.org> - 2017-09-23 15:10 +0200
    Re: [PATCH 00/33] x86 FPU fixes and cleanups for v4.14 Juergen Gross <jgross@suse.com> - 2017-09-23 17:10 +0200
      Re: [PATCH 00/33] x86 FPU fixes and cleanups for v4.14 Ingo Molnar <mingo@kernel.org> - 2017-09-24 01:30 +0200

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