From d353f82b2edae3019b0b9405976a05f18d120ce7 Mon Sep 17 00:00:00 2001 From: Jan Beulich Date: Tue, 14 Apr 2020 15:05:54 +0200 Subject: [PATCH] gnttab: fix GNTTABOP_copy continuation handling The XSA-226 fix was flawed - the backwards transformation on rc was done too early, causing a continuation to not get invoked when the need for preemption was determined at the very first iteration of the request. This in particular means that all of the status fields of the individual operations would be left untouched, i.e. set to whatever the caller may or may not have initialized them to. This is part of XSA-318. Reported-by: Pawel Wieczorkiewicz Signed-off-by: Jan Beulich Reviewed-by: Juergen Gross Tested-by: Pawel Wieczorkiewicz master commit: d6f22d5d9e8d6848ec229083ac9fb044f0adea93 master date: 2020-04-14 14:42:32 +0200 --- xen/common/grant_table.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/xen/common/grant_table.c b/xen/common/grant_table.c index e272daef5a..7d464a9641 100644 --- a/xen/common/grant_table.c +++ b/xen/common/grant_table.c @@ -3509,8 +3509,7 @@ do_grant_table_op( rc = gnttab_copy(copy, count); if ( rc > 0 ) { - rc = count - rc; - guest_handle_add_offset(copy, rc); + guest_handle_add_offset(copy, count - rc); uop = guest_handle_cast(copy, void); } break; @@ -3577,6 +3576,9 @@ do_grant_table_op( out: if ( rc > 0 || opaque_out != 0 ) { + /* Adjust rc, see gnttab_copy() for why this is needed. */ + if ( cmd == GNTTABOP_copy ) + rc = count - rc; ASSERT(rc < count); ASSERT((opaque_out & GNTTABOP_CMD_MASK) == 0); rc = hypercall_create_continuation(__HYPERVISOR_grant_table_op, "ihi", -- 2.39.5