From 6b1775f26a2da2b05a6dc8ec2b5d14e9a4701a1a Mon Sep 17 00:00:00 2001 From: Juergen Gross Date: Mon, 7 Mar 2022 09:48:54 +0100 Subject: xen/grant-table: add gnttab_try_end_foreign_access() Add a new grant table function gnttab_try_end_foreign_access(), which will remove and free a grant if it is not in use. Its main use case is to either free a grant if it is no longer in use, or to take some other action if it is still in use. This other action can be an error exit, or (e.g. in the case of blkfront persistent grant feature) some special handling. This is CVE-2022-23036, CVE-2022-23038 / part of XSA-396. Reported-by: Demi Marie Obenour Signed-off-by: Juergen Gross Reviewed-by: Jan Beulich --- V2: - new patch V4: - add comments to header (Jan Beulich) --- drivers/xen/grant-table.c | 14 ++++++++++++-- 1 file changed, 12 insertions(+), 2 deletions(-) (limited to 'drivers/xen/grant-table.c') diff --git a/drivers/xen/grant-table.c b/drivers/xen/grant-table.c index 3729bea0c989..1b82e7a3722a 100644 --- a/drivers/xen/grant-table.c +++ b/drivers/xen/grant-table.c @@ -435,11 +435,21 @@ static void gnttab_add_deferred(grant_ref_t ref, bool readonly, what, ref, page ? page_to_pfn(page) : -1); } +int gnttab_try_end_foreign_access(grant_ref_t ref) +{ + int ret = _gnttab_end_foreign_access_ref(ref, 0); + + if (ret) + put_free_entry(ref); + + return ret; +} +EXPORT_SYMBOL_GPL(gnttab_try_end_foreign_access); + void gnttab_end_foreign_access(grant_ref_t ref, int readonly, unsigned long page) { - if (gnttab_end_foreign_access_ref(ref, readonly)) { - put_free_entry(ref); + if (gnttab_try_end_foreign_access(ref)) { if (page != 0) put_page(virt_to_page(page)); } else -- cgit v1.2.3 From 1dbd11ca75fe664d3e54607547771d021f531f59 Mon Sep 17 00:00:00 2001 From: Juergen Gross Date: Mon, 7 Mar 2022 09:48:54 +0100 Subject: xen: remove gnttab_query_foreign_access() Remove gnttab_query_foreign_access(), as it is unused and unsafe to use. All previous use cases assumed a grant would not be in use after gnttab_query_foreign_access() returned 0. This information is useless in best case, as it only refers to a situation in the past, which could have changed already. Signed-off-by: Juergen Gross Reviewed-by: Jan Beulich --- drivers/xen/grant-table.c | 25 ------------------------- include/xen/grant_table.h | 2 -- 2 files changed, 27 deletions(-) (limited to 'drivers/xen/grant-table.c') diff --git a/drivers/xen/grant-table.c b/drivers/xen/grant-table.c index 1b82e7a3722a..e6548910e79f 100644 --- a/drivers/xen/grant-table.c +++ b/drivers/xen/grant-table.c @@ -133,13 +133,6 @@ struct gnttab_ops { * return the frame. */ unsigned long (*end_foreign_transfer_ref)(grant_ref_t ref); - /* - * Query the status of a grant entry. Ref parameter is reference of - * queried grant entry, return value is the status of queried entry. - * Detailed status(writing/reading) can be gotten from the return value - * by bit operations. - */ - int (*query_foreign_access)(grant_ref_t ref); }; struct unmap_refs_callback_data { @@ -284,22 +277,6 @@ int gnttab_grant_foreign_access(domid_t domid, unsigned long frame, } EXPORT_SYMBOL_GPL(gnttab_grant_foreign_access); -static int gnttab_query_foreign_access_v1(grant_ref_t ref) -{ - return gnttab_shared.v1[ref].flags & (GTF_reading|GTF_writing); -} - -static int gnttab_query_foreign_access_v2(grant_ref_t ref) -{ - return grstatus[ref] & (GTF_reading|GTF_writing); -} - -int gnttab_query_foreign_access(grant_ref_t ref) -{ - return gnttab_interface->query_foreign_access(ref); -} -EXPORT_SYMBOL_GPL(gnttab_query_foreign_access); - static int gnttab_end_foreign_access_ref_v1(grant_ref_t ref, int readonly) { u16 flags, nflags; @@ -1427,7 +1404,6 @@ static const struct gnttab_ops gnttab_v1_ops = { .update_entry = gnttab_update_entry_v1, .end_foreign_access_ref = gnttab_end_foreign_access_ref_v1, .end_foreign_transfer_ref = gnttab_end_foreign_transfer_ref_v1, - .query_foreign_access = gnttab_query_foreign_access_v1, }; static const struct gnttab_ops gnttab_v2_ops = { @@ -1439,7 +1415,6 @@ static const struct gnttab_ops gnttab_v2_ops = { .update_entry = gnttab_update_entry_v2, .end_foreign_access_ref = gnttab_end_foreign_access_ref_v2, .end_foreign_transfer_ref = gnttab_end_foreign_transfer_ref_v2, - .query_foreign_access = gnttab_query_foreign_access_v2, }; static bool gnttab_need_v2(void) diff --git a/include/xen/grant_table.h b/include/xen/grant_table.h index 358d2817741b..ab9e692a0ef4 100644 --- a/include/xen/grant_table.h +++ b/include/xen/grant_table.h @@ -125,8 +125,6 @@ int gnttab_grant_foreign_transfer(domid_t domid, unsigned long pfn); unsigned long gnttab_end_foreign_transfer_ref(grant_ref_t ref); unsigned long gnttab_end_foreign_transfer(grant_ref_t ref); -int gnttab_query_foreign_access(grant_ref_t ref); - /* * operations on reserved batches of grant references */ -- cgit v1.2.3 From 42baefac638f06314298087394b982ead9ec444b Mon Sep 17 00:00:00 2001 From: Juergen Gross Date: Mon, 7 Mar 2022 09:48:55 +0100 Subject: xen/gnttab: fix gnttab_end_foreign_access() without page specified gnttab_end_foreign_access() is used to free a grant reference and optionally to free the associated page. In case the grant is still in use by the other side processing is being deferred. This leads to a problem in case no page to be freed is specified by the caller: the caller doesn't know that the page is still mapped by the other side and thus should not be used for other purposes. The correct way to handle this situation is to take an additional reference to the granted page in case handling is being deferred and to drop that reference when the grant reference could be freed finally. This requires that there are no users of gnttab_end_foreign_access() left directly repurposing the granted page after the call, as this might result in clobbered data or information leaks via the not yet freed grant reference. This is part of CVE-2022-23041 / XSA-396. Reported-by: Simon Gaiser Signed-off-by: Juergen Gross Reviewed-by: Jan Beulich --- V4: - expand comment in header V5: - get page ref in case of kmalloc() failure, too --- drivers/xen/grant-table.c | 36 +++++++++++++++++++++++++++++------- include/xen/grant_table.h | 7 ++++++- 2 files changed, 35 insertions(+), 8 deletions(-) (limited to 'drivers/xen/grant-table.c') diff --git a/drivers/xen/grant-table.c b/drivers/xen/grant-table.c index e6548910e79f..5c83d41766c8 100644 --- a/drivers/xen/grant-table.c +++ b/drivers/xen/grant-table.c @@ -133,6 +133,10 @@ struct gnttab_ops { * return the frame. */ unsigned long (*end_foreign_transfer_ref)(grant_ref_t ref); + /* + * Read the frame number related to a given grant reference. + */ + unsigned long (*read_frame)(grant_ref_t ref); }; struct unmap_refs_callback_data { @@ -330,6 +334,16 @@ int gnttab_end_foreign_access_ref(grant_ref_t ref, int readonly) } EXPORT_SYMBOL_GPL(gnttab_end_foreign_access_ref); +static unsigned long gnttab_read_frame_v1(grant_ref_t ref) +{ + return gnttab_shared.v1[ref].frame; +} + +static unsigned long gnttab_read_frame_v2(grant_ref_t ref) +{ + return gnttab_shared.v2[ref].full_page.frame; +} + struct deferred_entry { struct list_head list; grant_ref_t ref; @@ -359,12 +373,9 @@ static void gnttab_handle_deferred(struct timer_list *unused) spin_unlock_irqrestore(&gnttab_list_lock, flags); if (_gnttab_end_foreign_access_ref(entry->ref, entry->ro)) { put_free_entry(entry->ref); - if (entry->page) { - pr_debug("freeing g.e. %#x (pfn %#lx)\n", - entry->ref, page_to_pfn(entry->page)); - put_page(entry->page); - } else - pr_info("freeing g.e. %#x\n", entry->ref); + pr_debug("freeing g.e. %#x (pfn %#lx)\n", + entry->ref, page_to_pfn(entry->page)); + put_page(entry->page); kfree(entry); entry = NULL; } else { @@ -389,9 +400,18 @@ static void gnttab_handle_deferred(struct timer_list *unused) static void gnttab_add_deferred(grant_ref_t ref, bool readonly, struct page *page) { - struct deferred_entry *entry = kmalloc(sizeof(*entry), GFP_ATOMIC); + struct deferred_entry *entry; + gfp_t gfp = (in_atomic() || irqs_disabled()) ? GFP_ATOMIC : GFP_KERNEL; const char *what = KERN_WARNING "leaking"; + entry = kmalloc(sizeof(*entry), gfp); + if (!page) { + unsigned long gfn = gnttab_interface->read_frame(ref); + + page = pfn_to_page(gfn_to_pfn(gfn)); + get_page(page); + } + if (entry) { unsigned long flags; @@ -1404,6 +1424,7 @@ static const struct gnttab_ops gnttab_v1_ops = { .update_entry = gnttab_update_entry_v1, .end_foreign_access_ref = gnttab_end_foreign_access_ref_v1, .end_foreign_transfer_ref = gnttab_end_foreign_transfer_ref_v1, + .read_frame = gnttab_read_frame_v1, }; static const struct gnttab_ops gnttab_v2_ops = { @@ -1415,6 +1436,7 @@ static const struct gnttab_ops gnttab_v2_ops = { .update_entry = gnttab_update_entry_v2, .end_foreign_access_ref = gnttab_end_foreign_access_ref_v2, .end_foreign_transfer_ref = gnttab_end_foreign_transfer_ref_v2, + .read_frame = gnttab_read_frame_v2, }; static bool gnttab_need_v2(void) diff --git a/include/xen/grant_table.h b/include/xen/grant_table.h index ab9e692a0ef4..c9fea9389ebe 100644 --- a/include/xen/grant_table.h +++ b/include/xen/grant_table.h @@ -107,7 +107,12 @@ int gnttab_end_foreign_access_ref(grant_ref_t ref, int readonly); * Note that the granted page might still be accessed (read or write) by the * other side after gnttab_end_foreign_access() returns, so even if page was * specified as 0 it is not allowed to just reuse the page for other - * purposes immediately. + * purposes immediately. gnttab_end_foreign_access() will take an additional + * reference to the granted page in this case, which is dropped only after + * the grant is no longer in use. + * This requires that multi page allocations for areas subject to + * gnttab_end_foreign_access() are done via alloc_pages_exact() (and freeing + * via free_pages_exact()) in order to avoid high order pages. */ void gnttab_end_foreign_access(grant_ref_t ref, int readonly, unsigned long page); -- cgit v1.2.3