From: Jarkko Sakkinen jarkko@kernel.org
mainline inclusion from mainline-v5.11 commit 2ade0d60939bcd54197c133b03b460fe62a4ec47 category: feature bugzilla: https://gitee.com/openeuler/kernel/issues/I4SIGI CVE: NA
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This has been shown in tests:
[ +0.000008] WARNING: CPU: 3 PID: 7620 at kernel/rcu/srcutree.c:374 cleanup_srcu_struct+0xed/0x100
This is essentially a use-after free, although SRCU notices it as an SRCU cleanup in an invalid context.
== Background ==
SGX has a data structure (struct sgx_encl_mm) which keeps per-mm SGX metadata. This is separate from struct sgx_encl because, in theory, an enclave can be mapped from more than one mm. sgx_encl_mm includes a pointer back to the sgx_encl.
This means that sgx_encl must have a longer lifetime than all of the sgx_encl_mm's that point to it. That's usually the case: sgx_encl_mm is freed only after the mmu_notifier is unregistered in sgx_release().
However, there's a race. If the process is exiting, sgx_mmu_notifier_release() can be called in parallel with sgx_release() instead of being called *by* it. The mmu_notifier path keeps encl_mm alive past when sgx_encl can be freed. This inverts the lifetime rules and means that sgx_mmu_notifier_release() can access a freed sgx_encl.
== Fix ==
Increase encl->refcount when encl_mm->encl is established. Release this reference when encl_mm is freed. This ensures that encl outlives encl_mm.
[ bp: Massage commit message. ]
Intel-SIG: commit 2ade0d60939b x86/sgx: Maintain encl->refcount for each encl->mm_list entry Backport for SGX Foundations support
Fixes: 1728ab54b4be ("x86/sgx: Add a page reclaimer") Reported-by: Haitao Huang haitao.huang@linux.intel.com Signed-off-by: Jarkko Sakkinen jarkko@kernel.org Signed-off-by: Borislav Petkov bp@suse.de Acked-by: Dave Hansen dave.hansen@linux.intel.com Link: https://lkml.kernel.org/r/20210207221401.29933-1-jarkko@kernel.org Signed-off-by: Fan Du fan.du@intel.com #openEuler_contributor Signed-off-by: Laibin Qiu qiulaibin@huawei.com --- arch/x86/kernel/cpu/sgx/driver.c | 3 +++ arch/x86/kernel/cpu/sgx/encl.c | 5 +++++ 2 files changed, 8 insertions(+)
diff --git a/arch/x86/kernel/cpu/sgx/driver.c b/arch/x86/kernel/cpu/sgx/driver.c index f2eac41bb4ff..8ce6d8371cfb 100644 --- a/arch/x86/kernel/cpu/sgx/driver.c +++ b/arch/x86/kernel/cpu/sgx/driver.c @@ -72,6 +72,9 @@ static int sgx_release(struct inode *inode, struct file *file) synchronize_srcu(&encl->srcu); mmu_notifier_unregister(&encl_mm->mmu_notifier, encl_mm->mm); kfree(encl_mm); + + /* 'encl_mm' is gone, put encl_mm->encl reference: */ + kref_put(&encl->refcount, sgx_encl_release); }
kref_put(&encl->refcount, sgx_encl_release); diff --git a/arch/x86/kernel/cpu/sgx/encl.c b/arch/x86/kernel/cpu/sgx/encl.c index 20a2dd5ba2b4..7449ef33f081 100644 --- a/arch/x86/kernel/cpu/sgx/encl.c +++ b/arch/x86/kernel/cpu/sgx/encl.c @@ -473,6 +473,9 @@ static void sgx_mmu_notifier_free(struct mmu_notifier *mn) { struct sgx_encl_mm *encl_mm = container_of(mn, struct sgx_encl_mm, mmu_notifier);
+ /* 'encl_mm' is going away, put encl_mm->encl reference: */ + kref_put(&encl_mm->encl->refcount, sgx_encl_release); + kfree(encl_mm); }
@@ -526,6 +529,8 @@ int sgx_encl_mm_add(struct sgx_encl *encl, struct mm_struct *mm) if (!encl_mm) return -ENOMEM;
+ /* Grab a refcount for the encl_mm->encl reference: */ + kref_get(&encl->refcount); encl_mm->encl = encl; encl_mm->mm = mm; encl_mm->mmu_notifier.ops = &sgx_mmu_notifier_ops;