Daniel Henrique Barboza <danielhb413@gmail.com> writes:
On 3/28/23 04:01, Markus Armbruster wrote:
Daniel Henrique Barboza <danielhb413@gmail.com> writes:
At this moment, arm_load_dtb() can free machine->fdt when
binfo->dtb_filename is NULL. If there's no 'dtb_filename', 'fdt' will be
retrieved by binfo->get_dtb(). If get_dtb() returns machine->fdt, as is
the case of machvirt_dtb() from hw/arm/virt.c, fdt now has a pointer to
machine->fdt. And, in that case, the existing g_free(fdt) at the end of
arm_load_dtb() will make machine->fdt point to an invalid memory region.
After the command 'dumpdtb' were introduced a couple of releases ago,
running it with any ARM machine that uses arm_load_dtb() will crash
QEMU.
Let's enable all arm_load_dtb() callers to use dumpdtb properly. Instead
of freeing 'fdt', assign it back to ms->fdt.
Note that all current callers (sbsa-ref.c, virt.c, xlnx-versal-virt.c)
are assigning ms->fdt before arm_load_dtb() is called, regardless of
whether the user is inputting an external FDT via '-dtb'. To avoid
leaking the board FDT if '-dtb' is used (since we're assigning ms->fdt
in the end), free ms->fdt before load_device_tree().
Cc: Peter Maydell <peter.maydell@linaro.org>
Cc: qemu-arm@nongnu.org
Fixes: bf353ad55590f ("qmp/hmp, device_tree.c: introduce dumpdtb")
Reported-by: Markus Armbruster <armbru@redhat.com>i
Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>
---
hw/arm/boot.c | 10 +++++++++-
1 file changed, 9 insertions(+), 1 deletion(-)
diff --git a/hw/arm/boot.c b/hw/arm/boot.c
index 50e5141116..de18c0a969 100644
--- a/hw/arm/boot.c
+++ b/hw/arm/boot.c
@@ -549,6 +549,13 @@ int arm_load_dtb(hwaddr addr, const struct arm_boot_info
*binfo,
goto fail;
}
+ /*
+ * If we're here we won't be using the ms->fdt from the board.
+ * We'll assign a new ms->fdt at the end, so free it now to
+ * avoid leaking the board FDT.
+ */
+ g_free(ms->fdt);
+
"We will" is not true: we will not if we goto fail. Leaves ms->fdt
dangling, doesn't it?
We can postpone this g_free() to execute after "if (!fdt) {}" to be sure that
we're
not freeing ms->fdt right before 'goto fail'.
Yes, but what about all the goto fail further down?
fdt = load_device_tree(filename, &size);
if (!fdt) {
fprintf(stderr, "Couldn't open dtb file %s\n", filename);
g_free(filename);
goto fail;
}
g_free(filename);
} else {
fdt = binfo->get_dtb(binfo, &size);
if (!fdt) {
fprintf(stderr, "Board was unable to create a dtb blob\n");
goto fail;
}
If we succeed, we'll assign @fdt to ms->fdt (next hunk). Won't this
leak old ms->fdt?
For all callers binfo->get_dtb() is returning ms->fdt, i.e. this line:
fdt = binfo->get_dtb(binfo, &size);
Is equal to this:
fdt = ms->fdt;
And this is why we can't unconditionally do a g_free(ms->fdt).
Uff. Not exactly obvious.
I believe we can improve the ARM boot code to not create ms->fdt at init(),
leaving it unassigned, and make get_dtb() return the machine FDT on a common
"void *" pointer. That would spare us from having go g_free(ms->fdt) to avoid
leaks and we would assign ms->fdt at the end of arm_load_dtb() normally. I made
a quick attempt at that but the ARM init() code is a little tricker than I've
anticipated. I might have a crack at it later.
Do we want a quick interim fix for 8.0?
Have a careful look at the untested patch below.
Thanks,
Daniel
}
@@ -689,7 +696,8 @@ int arm_load_dtb(hwaddr addr, const struct arm_boot_info
*binfo,
qemu_register_reset_nosnapshotload(qemu_fdt_randomize_seeds,
rom_ptr_for_as(as, addr, size));
- g_free(fdt);
+ /* Set ms->fdt for 'dumpdtb' QMP/HMP command */
+ ms->fdt = fdt;
return size;
diff --git a/hw/arm/boot.c b/hw/arm/boot.c
index 50e5141116..54f6a3e0b3 100644
--- a/hw/arm/boot.c
+++ b/hw/arm/boot.c
@@ -689,7 +689,10 @@ int arm_load_dtb(hwaddr addr, const struct arm_boot_info
*binfo,
qemu_register_reset_nosnapshotload(qemu_fdt_randomize_seeds,
rom_ptr_for_as(as, addr, size));
- g_free(fdt);
+ if (fdt != ms->fdt) {
+ g_free(ms->fdt);
+ ms->fdt = fdt;
+ }
return size;