[Qemu-devel] [PATCH] ahci.c: mask unused flags when reading size PRDT DBC

[reza . jelveh]

From: Reza Jelveh <reza.jel...@tuhh.de>

The data byte count(DBC) read from the description information is defined for
21:00. 30:22 are reserved and 31 is the Interrupt on Completion (I) flag.

Interrupt is not implemented in QEMU. tbl_entry_size is a signed integer and
improperly reading the DBC leads to a negative offset that causes sglist
allocation to fail.

Signed-off-by: Reza Jelveh <reza.jel...@tuhh.de>
---
 hw/ide/ahci.c | 12 +++++++++---
 hw/ide/ahci.h |  2 ++
 2 files changed, 11 insertions(+), 3 deletions(-)

diff --git a/hw/ide/ahci.c b/hw/ide/ahci.c
index 9bae22e..93aa981 100644
--- a/hw/ide/ahci.c
+++ b/hw/ide/ahci.c
@@ -639,6 +639,12 @@ static void ahci_write_fis_d2h(AHCIDevice *ad, uint8_t 
*cmd_fis)
     }
 }
 
+static int prdt_tbl_entry_size(const AHCI_SG tbl)
+{
+    return (le32_to_cpu(tbl.flags_size) & AHCI_PRDT_SIZE_MASK) + 1;
+}
+
+
 static int ahci_populate_sglist(AHCIDevice *ad, QEMUSGList *sglist, int offset)
 {
     AHCICmdHdr *cmd = ad->cur_cmd;
@@ -681,7 +687,7 @@ static int ahci_populate_sglist(AHCIDevice *ad, QEMUSGList 
*sglist, int offset)
         sum = 0;
         for (i = 0; i < sglist_alloc_hint; i++) {
             /* flags_size is zero-based */
-            tbl_entry_size = (le32_to_cpu(tbl[i].flags_size) + 1);
+            tbl_entry_size = prdt_tbl_entry_size(tbl[i]);
             if (offset <= (sum + tbl_entry_size)) {
                 off_idx = i;
                 off_pos = offset - sum;
@@ -700,12 +706,12 @@ static int ahci_populate_sglist(AHCIDevice *ad, 
QEMUSGList *sglist, int offset)
         qemu_sglist_init(sglist, qbus->parent, (sglist_alloc_hint - off_idx),
                          ad->hba->as);
         qemu_sglist_add(sglist, le64_to_cpu(tbl[off_idx].addr + off_pos),
-                        le32_to_cpu(tbl[off_idx].flags_size) + 1 - off_pos);
+                        prdt_tbl_entry_size(tbl[off_idx]) - off_pos);
 
         for (i = off_idx + 1; i < sglist_alloc_hint; i++) {
             /* flags_size is zero-based */
             qemu_sglist_add(sglist, le64_to_cpu(tbl[i].addr),
-                            le32_to_cpu(tbl[i].flags_size) + 1);
+                            prdt_tbl_entry_size(tbl[i]));
         }
     }
 
diff --git a/hw/ide/ahci.h b/hw/ide/ahci.h
index 9a4064f..f418b30 100644
--- a/hw/ide/ahci.h
+++ b/hw/ide/ahci.h
@@ -201,6 +201,8 @@
 
 #define AHCI_COMMAND_TABLE_ACMD            0x40
 
+#define AHCI_PRDT_SIZE_MASK                0x3fffff
+
 #define IDE_FEATURE_DMA                    1
 
 #define READ_FPDMA_QUEUED                  0x60
-- 
1.9.2