[Xen-changelog] [xen stable-4.6] tools/libxc: arm: Check the index before accessing the bank

[patchbot@xxxxxxx]

commit ae9bedcb9b23642896aa362e990fb740cd17d9cc
Author:     Julien Grall <julien.grall@xxxxxxxxxx>
AuthorDate: Thu Sep 17 18:36:36 2015 +0100
Commit:     Ian Campbell <ian.campbell@xxxxxxxxxx>
CommitDate: Mon Sep 28 16:40:29 2015 +0100

    tools/libxc: arm: Check the index before accessing the bank
    
    When creating a guest with more than 3GB of memory, the 2 banks will be
    used and the loop with overrunning. The code will fail later on because
    Xen will deny to populate the region:
    
    domainbuilder: detail: xc_dom_devicetree_mem: called
    domainbuilder: detail: xc_dom_mem_init: mem 3096 MB, pages 0xc1800 pages, 
4k each
    domainbuilder: detail: xc_dom_mem_init: 0xc1800 pages
    domainbuilder: detail: xc_dom_boot_mem_init: called
    domainbuilder: detail: set_mode: guest xen-3.0-aarch64, address size 64
    domainbuilder: detail: xc_dom_malloc            : 14384 kB
    domainbuilder: detail: populate_guest_memory: populating RAM 
@0000000040000000-0000000100000000 (3072MB)
    domainbuilder: detail: populate_one_size: populated 0x3/0x3 entries with 
shift 18
    domainbuilder: detail: populate_guest_memory: populating RAM 
@0000000200000000-0000000201800000 (24MB)
    domainbuilder: detail: populate_one_size: populated 0xc/0xc entries with 
shift 9
    domainbuilder: detail: populate_guest_memory: populating RAM 
@0000007fad41c000-0007fb39dd42c000 (2141954816MB)
    domainbuilder: detail: populate_one_size: populated 0x100/0x1e4 entries 
with shift 0
    domainbuilder: detail: populate_guest_memory: Not enough RAM
    
    This is because we are currently accessing the bank before checking the
    validity of the index. AFAICT, on  Debian Jessie, the compiler (gcc 4.9.2) 
is
    assuming that it's not necessary to verify the index because it's used
    before. This is a valid assumption because the operand of && are
    execute from from left to right.
    
    Re-order the checks to verify the validity of the index before accessing
    the bank.
    
    The problem has been present since the introduction of the multi-bank
    feature in commit 45d9867837f099e9eed4189dac5ed39d1fe2ed49 " tools: arm:
    prepare domain builder for multiple banks of guest RAM".
    
    Signed-off-by: Julien Grall <julien.grall@xxxxxxxxxx>
    Acked-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
    (cherry picked from commit ed5c2c05cfa557b2391aef9557864d8d958d8d84)
---
 tools/libxc/xc_dom_arm.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/tools/libxc/xc_dom_arm.c b/tools/libxc/xc_dom_arm.c
index b00d667..aeaba54 100644
--- a/tools/libxc/xc_dom_arm.c
+++ b/tools/libxc/xc_dom_arm.c
@@ -460,7 +460,7 @@ int arch_setup_meminit(struct xc_dom_image *dom)
         dom->p2m_host[pfn] = INVALID_P2M_ENTRY;
 
     /* setup initial p2m and allocate guest memory */
-    for ( i = 0; dom->rambank_size[i] && i < GUEST_RAM_BANKS; i++ )
+    for ( i = 0; i < GUEST_RAM_BANKS && dom->rambank_size[i]; i++ )
     {
         if ((rc = populate_guest_memory(dom,
                                         bankbase[i] >> XC_PAGE_SHIFT,
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.6

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