| Message ID | 20201005031759.143544-1-jarkko.sakkinen@linux.intel.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [v2] Fix the issue further discussed in: | expand |
On Mon, Oct 05, 2020 at 06:17:59AM +0300, Jarkko Sakkinen wrote: > @@ -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; This really doesn't do what you think it does. int ret = 0; int count = 0; xas_lock(&xas); while (xas.index < idx_end) { struct sgx_page *page = xas_next(&xas); if (!page || (~page->vm_max_prot_bits & vm_prot_bits)) { ret = -EACCESS; break; } if (++count % XA_CHECK_SCHED) continue; xas_pause(&xas); xas_unlock(&xas); cond_resched(); xas_lock(&xas); } xas_unlock(&xas); return ret;
On Mon, Oct 05, 2020 at 12:11:39PM +0100, Matthew Wilcox wrote: > On Mon, Oct 05, 2020 at 06:17:59AM +0300, Jarkko Sakkinen wrote: > > @@ -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; > > This really doesn't do what you think it does. > > int ret = 0; > int count = 0; > > xas_lock(&xas); > while (xas.index < idx_end) { > struct sgx_page *page = xas_next(&xas); > > if (!page || (~page->vm_max_prot_bits & vm_prot_bits)) { > ret = -EACCESS; > break; > } > > if (++count % XA_CHECK_SCHED) > continue; > xas_pause(&xas); > xas_unlock(&xas); > cond_resched(); > xas_lock(&xas); > } > xas_unlock(&xas); > > return ret; No mine certainly does not, it locks up the system if the loop succeeds (i.e. does not return -EACCESS) :-) Unfortunately had by mistake the v1 patch (xa_load()) in the kernel that I used to test. /Jarkko
On Mon, Oct 05, 2020 at 02:48:07PM +0300, Jarkko Sakkinen wrote: > On Mon, Oct 05, 2020 at 12:11:39PM +0100, Matthew Wilcox wrote: > > On Mon, Oct 05, 2020 at 06:17:59AM +0300, Jarkko Sakkinen wrote: > > > @@ -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; > > > > This really doesn't do what you think it does. > > > > int ret = 0; > > int count = 0; > > > > xas_lock(&xas); > > while (xas.index < idx_end) { > > struct sgx_page *page = xas_next(&xas); > > > > if (!page || (~page->vm_max_prot_bits & vm_prot_bits)) { > > ret = -EACCESS; > > break; > > } > > > > if (++count % XA_CHECK_SCHED) > > continue; > > xas_pause(&xas); > > xas_unlock(&xas); > > cond_resched(); > > xas_lock(&xas); > > } > > xas_unlock(&xas); > > > > return ret; > > No mine certainly does not, it locks up the system if the loop succeeds > (i.e. does not return -EACCESS) :-) Unfortunately had by mistake the v1 > patch (xa_load()) in the kernel that I used to test. ... and not having xas_unlock() in the end was not intentional. /Jarkko
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; }
1. https://lore.kernel.org/linux-sgx/op.0rwbv916wjvjmi@mqcpg7oapc828.gar.corp.intel.com/ 2. https://lore.kernel.org/linux-sgx/20201003195440.GD20115@casper.infradead.org/ Use the approach suggested by Matthew, and supported by the analysis that I wrote: https://lore.kernel.org/linux-sgx/20201005030619.GA126283@linux.intel.com/ Reported-by: Haitao Huang <haitao.huang@linux.intel.com> Suggested-by: Matthew Wilcox <willy@infradead.org> Cc: Sean Christopherson <sean.j.christopherson@intel.com> Cc: Jethro Beekman <jethro@fortanix.com> Cc: Dave Hansen <dave.hansen@linux.intel.com> Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com> --- arch/x86/kernel/cpu/sgx/encl.c | 24 +++++++++++++++++++++++- 1 file changed, 23 insertions(+), 1 deletion(-)