4.18-stable review patch. If anyone has any objections, please let me know.
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From: Frederic Barrat fbarrat@linux.ibm.com
commit d497ebf5fb3a026c0817f8c96cde578787f24093 upstream.
If a process exits without doing proper cleanup, there's a window where an opencapi device can try to access the memory of the dying process and may trigger a page fault. That's an expected scenario and the ocxl driver holds a reference on the mm_struct of the process until the opencapi device is notified of the process exiting. However, if mm_users is already at 0, i.e. the address space of the process has already been destroyed, the driver shouldn't try resolving the page fault, as it will fail, but it can also try accessing already freed data.
It is fixed by only calling the bottom half of the page fault handler if mm_users is greater than 0 and get a reference on mm_users instead of mm_count. Otherwise, we can safely return a translation fault to the device, as its associated memory context is being removed. The opencapi device will be properly cleaned up shortly after when closing the file descriptors.
Fixes: 5ef3166e8a32 ("ocxl: Driver code for 'generic' opencapi devices") Cc: stable@vger.kernel.org # v4.16+ Signed-off-by: Frederic Barrat fbarrat@linux.ibm.com Reviewed-By: Alastair D'Silva alastair@d-silva.org Acked-by: Andrew Donnellan andrew.donnellan@au1.ibm.com Signed-off-by: Michael Ellerman mpe@ellerman.id.au Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- drivers/misc/ocxl/link.c | 24 +++++++++++++++--------- 1 file changed, 15 insertions(+), 9 deletions(-)
--- a/drivers/misc/ocxl/link.c +++ b/drivers/misc/ocxl/link.c @@ -136,7 +136,7 @@ static void xsl_fault_handler_bh(struct int rc;
/* - * We need to release a reference on the mm whenever exiting this + * We must release a reference on mm_users whenever exiting this * function (taken in the memory fault interrupt handler) */ rc = copro_handle_mm_fault(fault->pe_data.mm, fault->dar, fault->dsisr, @@ -172,7 +172,7 @@ static void xsl_fault_handler_bh(struct } r = RESTART; ack: - mmdrop(fault->pe_data.mm); + mmput(fault->pe_data.mm); ack_irq(spa, r); }
@@ -184,6 +184,7 @@ static irqreturn_t xsl_fault_handler(int struct pe_data *pe_data; struct ocxl_process_element *pe; int lpid, pid, tid; + bool schedule = false;
read_irq(spa, &dsisr, &dar, &pe_handle); trace_ocxl_fault(spa->spa_mem, pe_handle, dsisr, dar, -1); @@ -226,14 +227,19 @@ static irqreturn_t xsl_fault_handler(int } WARN_ON(pe_data->mm->context.id != pid);
- spa->xsl_fault.pe = pe_handle; - spa->xsl_fault.dar = dar; - spa->xsl_fault.dsisr = dsisr; - spa->xsl_fault.pe_data = *pe_data; - mmgrab(pe_data->mm); /* mm count is released by bottom half */ - + if (mmget_not_zero(pe_data->mm)) { + spa->xsl_fault.pe = pe_handle; + spa->xsl_fault.dar = dar; + spa->xsl_fault.dsisr = dsisr; + spa->xsl_fault.pe_data = *pe_data; + schedule = true; + /* mm_users count released by bottom half */ + } rcu_read_unlock(); - schedule_work(&spa->xsl_fault.fault_work); + if (schedule) + schedule_work(&spa->xsl_fault.fault_work); + else + ack_irq(spa, ADDRESS_ERROR); return IRQ_HANDLED; }