From: "Chang S. Bae" <chang.seok.bae@intel.com>
To: linux-kernel@vger.kernel.org
Cc: x86@kernel.org, tglx@linutronix.de, mingo@redhat.com,
bp@alien8.de, dave.hansen@linux.intel.com, hpa@zytor.com,
yuan.yao@intel.com, chang.seok.bae@intel.com
Subject: [PATCH v2] x86/fpu: Fix copy_xstate_to_uabi() to copy init states correctly
Date: Fri, 21 Oct 2022 11:58:44 -0700 [thread overview]
Message-ID: <20221021185844.13472-1-chang.seok.bae@intel.com> (raw)
In-Reply-To: <20221018221349.4196-2-chang.seok.bae@intel.com>
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>
Tested-by: Yuan Yao <yuan.yao@intel.com>
Cc: x86@kernel.org
Cc: linux-kernel@vger.kernel.org
Link: https://lore.kernel.org/lkml/BYAPR11MB3717EDEF2351C958F2C86EED95259@BYAPR11MB3717.namprd11.prod.outlook.com/
---
Change from v1:
* Adjust the 'mask' instead of the loop iteration code (Dave Hansen).
The context of this along with the init_fpstate fix was described in the v1
cover letter:
https://lore.kernel.org/lkml/20221018221349.4196-1-chang.seok.bae@intel.com/
---
arch/x86/kernel/fpu/xstate.c | 9 +++++++++
1 file changed, 9 insertions(+)
diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c
index e77cabfa802f..59e543b95a3c 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
--
2.17.1
next prev parent reply other threads:[~2022-10-21 19:09 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-08-24 19:12 [PATCH 0/3] x86/fpu: Improve the init_fpstate setup code Chang S. Bae
2022-08-24 19:12 ` [PATCH 1/3] x86/fpu: Configure init_fpstate attributes orderly Chang S. Bae
2022-10-03 21:18 ` Neel Natu
2022-10-17 13:47 ` [tip: x86/urgent] " tip-bot2 for Chang S. Bae
2022-08-24 19:12 ` [PATCH 2/3] x86/fpu: Fix the init_fpstate size check with the actual size Chang S. Bae
2022-10-17 13:47 ` [tip: x86/urgent] " tip-bot2 for Chang S. Bae
2022-08-24 19:12 ` [PATCH 3/3] x86/fpu: Exclude dynamic states from init_fpstate Chang S. Bae
2022-10-17 13:47 ` [tip: x86/urgent] " tip-bot2 for Chang S. Bae
2022-10-18 22:13 ` [PATCH 0/1] x86/fpu: Follow up on the init_fpstate fix Chang S. Bae
2022-10-18 22:13 ` [PATCH 1/1] x86/fpu: Fix copy_xstate_to_uabi() to copy init states correctly Chang S. Bae
2022-10-20 16:57 ` Dave Hansen
2022-10-20 18:52 ` Chang S. Bae
2022-10-21 18:58 ` Chang S. Bae [this message]
2022-10-21 22:25 ` [tip: x86/urgent] " tip-bot2 for Chang S. Bae
2022-10-22 6:23 ` Ingo Molnar
2022-10-22 13:02 ` Chang S. Bae
2023-02-27 21:05 ` [PATCH 0/2] x86/fpu/xstate: Follow up on the init_fpstate fallout again Chang S. Bae
2023-02-27 21:05 ` [PATCH 1/2] x86/fpu/xstate: Prevent false-positive warning in __copy_xstate_uabi_buf() Chang S. Bae
2023-02-27 21:05 ` [PATCH 2/2] selftests/x86/amx: Add a ptrace test Chang S. Bae
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