diff mbox series

[tip:,x86/urgent] x86/fpu: Fix copy_xstate_to_uabi() to copy init states correctly

Message ID 166639111821.401.9381657733834636095.tip-bot2@tip-bot2
State New
Headers
Series [tip:,x86/urgent] x86/fpu: Fix copy_xstate_to_uabi() to copy init states correctly |

Commit Message

tip-bot2 for Thomas Gleixner Oct. 21, 2022, 10:25 p.m. UTC 
  The following commit has been merged into the x86/urgent branch of tip:

Commit-ID:     471f0aa7fa64e23766a1473b32d9ec3f0718895a
Gitweb:        https://git.kernel.org/tip/471f0aa7fa64e23766a1473b32d9ec3f0718895a
Author:        Chang S. Bae <chang.seok.bae@intel.com>
AuthorDate:    Fri, 21 Oct 2022 11:58:44 -07:00
Committer:     Dave Hansen <dave.hansen@linux.intel.com>
CommitterDate: Fri, 21 Oct 2022 15:22:09 -07:00

x86/fpu: Fix copy_xstate_to_uabi() to copy init states correctly

When an extended state component is not present in fpstate, but in init
state, the function copies from init_fpstate via copy_feature().

But, dynamic states are not present in init_fpstate because of all-zeros
init states. Then retrieving them from init_fpstate will explode like this:

 BUG: kernel NULL pointer dereference, address: 0000000000000000
 ...
 RIP: 0010:memcpy_erms+0x6/0x10
  ? __copy_xstate_to_uabi_buf+0x381/0x870
  fpu_copy_guest_fpstate_to_uabi+0x28/0x80
  kvm_arch_vcpu_ioctl+0x14c/0x1460 [kvm]
  ? __this_cpu_preempt_check+0x13/0x20
  ? vmx_vcpu_put+0x2e/0x260 [kvm_intel]
  kvm_vcpu_ioctl+0xea/0x6b0 [kvm]
  ? kvm_vcpu_ioctl+0xea/0x6b0 [kvm]
  ? __fget_light+0xd4/0x130
  __x64_sys_ioctl+0xe3/0x910
  ? debug_smp_processor_id+0x17/0x20
  ? fpregs_assert_state_consistent+0x27/0x50
  do_syscall_64+0x3f/0x90
  entry_SYSCALL_64_after_hwframe+0x63/0xcd

Adjust the 'mask' to zero out the userspace buffer for the features that
are not available both from fpstate and from init_fpstate.

The dynamic features depend on the compacted XSAVE format. Ensure it is
enabled before reading XCOMP_BV in init_fpstate.

Fixes: 2308ee57d93d ("x86/fpu/amx: Enable the AMX feature in 64-bit mode")
Reported-by: Yuan Yao <yuan.yao@intel.com>
Suggested-by: Dave Hansen <dave.hansen@intel.com>
Signed-off-by: Chang S. Bae <chang.seok.bae@intel.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Tested-by: Yuan Yao <yuan.yao@intel.com>
Link: https://lore.kernel.org/lkml/BYAPR11MB3717EDEF2351C958F2C86EED95259@BYAPR11MB3717.namprd11.prod.outlook.com/
Link: https://lkml.kernel.org/r/20221021185844.13472-1-chang.seok.bae@intel.com
---
 arch/x86/kernel/fpu/xstate.c |  9 +++++++++
 1 file changed, 9 insertions(+)

Comments

Ingo Molnar Oct. 22, 2022, 6:23 a.m. UTC | #1 
* tip-bot2 for Chang S. Bae <tip-bot2@linutronix.de> wrote:

> The following commit has been merged into the x86/urgent branch of tip:
> 
> Commit-ID:     471f0aa7fa64e23766a1473b32d9ec3f0718895a
> Gitweb:        https://git.kernel.org/tip/471f0aa7fa64e23766a1473b32d9ec3f0718895a
> Author:        Chang S. Bae <chang.seok.bae@intel.com>
> AuthorDate:    Fri, 21 Oct 2022 11:58:44 -07:00
> Committer:     Dave Hansen <dave.hansen@linux.intel.com>
> CommitterDate: Fri, 21 Oct 2022 15:22:09 -07:00
> 
> x86/fpu: Fix copy_xstate_to_uabi() to copy init states correctly

> +		mask &= (header.xfeatures | xinit->header.xcomp_bv);

Nit: those parentheses are not needed.

Thanks,

	Ingo
Chang S. Bae Oct. 22, 2022, 1:02 p.m. UTC | #2 
On 10/21/2022 11:23 PM, Ingo Molnar wrote:
> 
> Nit: those parentheses are not needed.

Ah, right.

Sorry, let me follow up on this later.

Thanks,
Chang
diff mbox series

Patch

diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c
index e77cabf..59e543b 100644
--- a/arch/x86/kernel/fpu/xstate.c
+++ b/arch/x86/kernel/fpu/xstate.c
@@ -1125,6 +1125,15 @@  void __copy_xstate_to_uabi_buf(struct membuf to, struct fpstate *fpstate,
 	 */
 	mask = fpstate->user_xfeatures;
 
+	/*
+	 * Dynamic features are not present in init_fpstate. When they are
+	 * in an all zeros init state, remove those from 'mask' to zero
+	 * those features in the user buffer instead of retrieving them
+	 * from init_fpstate.
+	 */
+	if (fpu_state_size_dynamic())
+		mask &= (header.xfeatures | xinit->header.xcomp_bv);
+
 	for_each_extended_xfeature(i, mask) {
 		/*
 		 * If there was a feature or alignment gap, zero the space