Fix the issue further discussed in: 1. https://lore.kernel.org/linux-sgx/op.0rwbv916wjvjmi@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/ 2. https://lore.kernel.org/linux-sgx/20201003195440.GD20115@xxxxxxxxxxxxxxxxxxxx/ Use the approach suggested by Matthew, and supported by the analysis that I wrote: https://lore.kernel.org/linux-sgx/20201005030619.GA126283@xxxxxxxxxxxxxxx/ Reported-by: Haitao Huang <haitao.huang@xxxxxxxxxxxxxxx> Suggested-by: Matthew Wilcox <willy@xxxxxxxxxxxxx> Cc: Sean Christopherson <sean.j.christopherson@xxxxxxxxx> Cc: Jethro Beekman <jethro@xxxxxxxxxxxx> Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx> Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@xxxxxxxxxxxxxxx> --- arch/x86/kernel/cpu/sgx/encl.c | 24 +++++++++++++++++++++++- 1 file changed, 23 insertions(+), 1 deletion(-) diff --git a/arch/x86/kernel/cpu/sgx/encl.c b/arch/x86/kernel/cpu/sgx/encl.c index 4c6407cd857a..2bb3ec6996e9 100644 --- a/arch/x86/kernel/cpu/sgx/encl.c +++ b/arch/x86/kernel/cpu/sgx/encl.c @@ -307,6 +307,7 @@ int sgx_encl_may_map(struct sgx_encl *encl, unsigned long start, unsigned long idx_start = PFN_DOWN(start); unsigned long idx_end = PFN_DOWN(end - 1); struct sgx_encl_page *page; + unsigned long count = 0; XA_STATE(xas, &encl->page_array, idx_start); @@ -317,10 +318,31 @@ int sgx_encl_may_map(struct sgx_encl *encl, unsigned long start, if (current->personality & READ_IMPLIES_EXEC) return -EACCES; - xas_for_each(&xas, page, idx_end) + /* + * No need to hold encl->lock: + * 1. None of the page->* get written. + * 2. page->vm_max_prot_bits is set in sgx_encl_page_alloc(). This + * is before calling xa_insert(). After that it is never modified. + */ + xas_lock(&xas); + xas_for_each(&xas, page, idx_end) { + if (++count % XA_CHECK_SCHED) + continue; + + xas_pause(&xas); + xas_unlock(&xas); + + /* + * Attributes are not protected by the xa_lock, so I'm assuming + * that this is the legit place for the check. + */ if (!page || (~page->vm_max_prot_bits & vm_prot_bits)) return -EACCES; + cond_resched(); + xas_lock(&xas); + } + return 0; } -- 2.25.1
