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[Qemu-devel] [PATCH 34/42] tpm-passthrough: workaround a possible race
From: |
Marc-André Lureau |
Subject: |
[Qemu-devel] [PATCH 34/42] tpm-passthrough: workaround a possible race |
Date: |
Tue, 10 Oct 2017 00:56:15 +0200 |
The TPM backend processing thread has common shared variable race
issues. (they should not be so easy to reach since guest interaction
with the device is slow compared to host emulation)
An obvious one is setting op_cancelled from device thread after
calling write(cancel_fd). The backend thread may return before the
device thread has set the variable. Instead set it before
cancellation. Even if the write() failed, the end result is command
get possibly cancelled (even if cancellation came from external
sources it doesn't matter much).
It's worth to consider removing the backend processing thread for now.
Signed-off-by: Marc-André Lureau <address@hidden>
---
hw/tpm/tpm_passthrough.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/hw/tpm/tpm_passthrough.c b/hw/tpm/tpm_passthrough.c
index 0806cf86af..d71d64e8aa 100644
--- a/hw/tpm/tpm_passthrough.c
+++ b/hw/tpm/tpm_passthrough.c
@@ -89,6 +89,7 @@ static int tpm_passthrough_unix_tx_bufs(TPMPassthruState
*tpm_pt,
bool is_selftest;
const struct tpm_resp_hdr *hdr;
+ /* FIXME: protect shared variables or use other sync mechanism */
tpm_pt->tpm_op_canceled = false;
tpm_pt->tpm_executing = true;
*selftest_done = false;
@@ -178,12 +179,11 @@ static void tpm_passthrough_cancel_cmd(TPMBackend *tb)
*/
if (tpm_pt->tpm_executing) {
if (tpm_pt->cancel_fd >= 0) {
+ tpm_pt->tpm_op_canceled = true;
n = write(tpm_pt->cancel_fd, "-", 1);
if (n != 1) {
error_report("Canceling TPM command failed: %s",
strerror(errno));
- } else {
- tpm_pt->tpm_op_canceled = true;
}
} else {
error_report("Cannot cancel TPM command due to missing "
--
2.14.1.146.gd35faa819
- Re: [Qemu-devel] [PATCH 31/42] tpm-backend: move set 'id' to common code, (continued)
Re: [Qemu-devel] [PATCH 31/42] tpm-backend: move set 'id' to common code, Stefan Berger, 2017/10/10
[Qemu-devel] [PATCH 32/42] tpm-passthrough: make it safer to destroy after creation, Marc-André Lureau, 2017/10/09
[Qemu-devel] [PATCH 33/42] tpm-passthrough: remove error cleanup from handle_device_opts, Marc-André Lureau, 2017/10/09
[Qemu-devel] [PATCH 35/42] tpm-tis: simplify header inclusion, Marc-André Lureau, 2017/10/09
[Qemu-devel] [PATCH 34/42] tpm-passthrough: workaround a possible race,
Marc-André Lureau <=
[Qemu-devel] [PATCH 36/42] tpm: rename qemu_find_tpm() -> qemu_find_tpm_be(), Marc-André Lureau, 2017/10/09
[Qemu-devel] [PATCH 37/42] tpm: lookup the the TPM interface instead of TIS device, Marc-André Lureau, 2017/10/09
Re: [Qemu-devel] [PATCH 37/42] tpm: lookup the the TPM interface instead of TIS device, Stefan Berger, 2017/10/10
[Qemu-devel] [PATCH 38/42] tpm: add TPM interface to lookup TPM version, Marc-André Lureau, 2017/10/09