Can you run this in a KVM ? My go-to is virtme-ng, where I can run my hacks on my laptop, in its own VM - on a copy of my whole system. with the tools I'm familiar with. then you can attach gdb to the VM. then Id try a watchpoint on the memory. On Fri, Nov 15, 2024 at 11:19 AM Muni Sekhar <munisekharrms@gmail.com> wrote:
Hi all,
I am encountering a memory corruption issue in the function msm_set_laddr() from the Slimbus MSM Controller driver source code. https://android.googlesource.com/kernel/msm/+/refs/heads/android-msm-sunfish...
In msm_set_laddr(), one of the arguments is ea (enumeration address), which is a pointer to constant data. While testing, I observed strange behavior:
The contents of the ea buffer get corrupted during a timeout scenario in the call to:
timeout = wait_for_completion_timeout(&done, HZ);
Specifically, the ea buffer's contents differ before and after the wait_for_completion_timeout() call, even though it's declared as a pointer to constant data (const u8 *ea). To debug this issue, I enabled KASAN, but it didn't reveal any memory corruption. After the buffer corruption, random memory allocations in other parts of the kernel occasionally result in a GPF crash.
Here is the relevant part of the code:
static int msm_set_laddr(struct slim_controller *ctrl, const u8 *ea, u8 elen, u8 laddr) { struct msm_slim_ctrl *dev = slim_get_ctrldata(ctrl); struct completion done; int timeout, ret, retries = 0; u32 *buf; retry_laddr: init_completion(&done); mutex_lock(&dev->tx_lock); buf = msm_get_msg_buf(dev, 9, &done); if (buf == NULL) return -ENOMEM; buf[0] = SLIM_MSG_ASM_FIRST_WORD(9, SLIM_MSG_MT_CORE, SLIM_MSG_MC_ASSIGN_LOGICAL_ADDRESS, SLIM_MSG_DEST_LOGICALADDR, ea[5] | ea[4] << 8); buf[1] = ea[3] | (ea[2] << 8) | (ea[1] << 16) | (ea[0] << 24); buf[2] = laddr; ret = msm_send_msg_buf(dev, buf, 9, MGR_TX_MSG); timeout = wait_for_completion_timeout(&done, HZ); if (!timeout) dev->err = -ETIMEDOUT; if (dev->err) { ret = dev->err; dev->err = 0; } mutex_unlock(&dev->tx_lock); if (ret) { pr_err("set LADDR:0x%x failed:ret:%d, retrying", laddr, ret); if (retries < INIT_MX_RETRIES) { msm_slim_wait_retry(dev); retries++; goto retry_laddr; } else { pr_err("set LADDR failed after retrying:ret:%d", ret); } } return ret; }
What I've Tried: KASAN: Enabled it but couldn't identify the source of the corruption. Debugging Logs: Added logs to print the ea contents before and after the wait_for_completion_timeout() call. The logs show a mismatch in the data.
Question: How can I efficiently trace the source of the memory corruption in this scenario? Could wait_for_completion_timeout() or a related function cause unintended side effects? Are there additional tools or techniques (e.g., dynamic debugging or specific kernel config options) that can help identify this corruption? Any insights or suggestions would be greatly appreciated!
-- Thanks, Sekhar
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