[PATCH 01/15] hw/ide: reject an unsupported CHS translation

From: Denis V. Lunev <[email protected]>

ide_set_sector() divides by (s->heads * s->sectors) when the drive is
addressed in CHS mode. Both come from the guest via INITIALIZE DEVICE
PARAMETERS, and cmd_specify() stored them without any check, so a guest
asking for zero sectors per logical track killed QEMU with SIGFPE on the
completion of the first CHS read or write. s->heads is safe, as the
command passes a heads-1 value.

The count has an upper bound as well. The legacy sector count register is
eight bits wide, but handle_cmd() takes the count from a 16 bit field of
the register FIS, so an AHCI guest can ask for up to 65535 sectors per
track, and the CHS branch of ide_get_sector() then overflows the int it
multiplies cylinder, heads and sectors in.

ATA-5 6.2 numbers CHS sectors from one and ATA-2 D.2.8 limits IDENTIFY
DEVICE word 56 to 1 through 255, so neither end is a translation a device
may accept. ATA-5 8.16.6 requires an unsupported one to be reported as an
aborted command: do that, leave the translation in effect alone, and
refuse the value rather than checking it at every use.

Cc: John Snow <[email protected]>
Cc: Peter Maydell <[email protected]>
Fixes: 176e4961bb33 ("hw/ide/core.c: Implement ATA INITIALIZE_DEVICE_PARAMETERS command")
Reported-by: Zheyu Ma <[email protected]>
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/2399
Signed-off-by: Denis V. Lunev <[email protected]>
---
 hw/ide/core.c | 17 ++++++++++++-----
 1 file changed, 12 insertions(+), 5 deletions(-)

diff --git a/hw/ide/core.c b/hw/ide/core.c
index fb9bf11b45..747fa71677 100644
--- a/hw/ide/core.c
+++ b/hw/ide/core.c
@@ -1655,14 +1655,21 @@ static bool cmd_check_power_mode(IDEState *s, uint8_t cmd)
 /* INITIALIZE DEVICE PARAMETERS */
 static bool cmd_specify(IDEState *s, uint8_t cmd)
 {
-    if (s->blk && s->drive_kind != IDE_CD) {
-        s->heads = (s->select & (ATA_DEV_HS)) + 1;
-        s->sectors = s->nsector;
-        ide_bus_set_irq(s->bus);
-    } else {
+    if (!s->blk || s->drive_kind == IDE_CD) {
+        ide_abort_command(s);
+        return true;
+    }
+
+    /* ATA-2 D.2.8 limits IDENTIFY DEVICE word 56, and the count, to 1..255 */
+    if (s->nsector == 0 || s->nsector > 255) {
         ide_abort_command(s);
+        return true;
     }
 
+    s->heads = (s->select & (ATA_DEV_HS)) + 1;
+    s->sectors = s->nsector;
+    ide_bus_set_irq(s->bus);
+
     return true;
 }
 
-- 
2.53.0