Re: [RFC v2 1/2] riscv: allow resume after exception

On 10/31/23 09:53, Xiang W wrote:

setjmp can be called in set_resume.

Unfortunately this is not possible. A longjmp buffer only stores register values and not the stack content.

Let's assume that setjmp() is moved into set_resume():

Let a function call set_resume(). The caller's address will be on the stack. Once the set_resume returns and the caller invokes another function the original stack content will be overwritten. When an exception occurs the longjmp will reenter set_resume() with the original stack pointer value pointing to a stack that does not match the original call to set_resume and set_resume will return to a random address.

Best regards

Heinrich

Regards, Xiang W

Heinrich Schuchardt heinrich.schuchardt@canonical.com 于2023年10月29日周日 16:56写道：

...

If CSRs like seed are readable by S-mode, may not be determinable by S-mode. For safe driver probing allow to resume via a longjmp after an exception.

Signed-off-by: Heinrich Schuchardt heinrich.schuchardt@canonical.com

v2: new patch

---

arch/riscv/lib/interrupts.c | 13 +++++++++++++ include/interrupt.h | 22 ++++++++++++++++++++++ 2 files changed, 35 insertions(+) create mode 100644 include/interrupt.h

diff --git a/arch/riscv/lib/interrupts.c b/arch/riscv/lib/interrupts.c index 02dbcfd423..a26ccc721f 100644 --- a/arch/riscv/lib/interrupts.c +++ b/arch/riscv/lib/interrupts.c @@ -12,6 +12,7 @@ #include <linux/compat.h> #include <efi_loader.h> #include <hang.h> +#include <interrupt.h> #include <irq_func.h> #include <asm/global_data.h> #include <asm/ptrace.h> @@ -21,6 +22,13 @@

DECLARE_GLOBAL_DATA_PTR;

+static struct resume_data *resume;

+void set_resume(struct resume_data *data) +{

•   resume = data;
  

+}

• static void show_efi_loaded_images(uintptr_t epc) { efi_print_image_infos((void *)epc);

@@ -105,6 +113,11 @@ static void _exit_trap(ulong code, ulong epc, ulong tval, struct pt_regs *regs) "Store/AMO page fault", };

•   if (resume) {
  

•           resume->code = code;
  

•           longjmp(resume->jump, 1);
  

•   }
  

•    if (code < ARRAY_SIZE(exception_code))
             printf("Unhandled exception: %s\n", exception_code[code]);
     else
  

diff --git a/include/interrupt.h b/include/interrupt.h new file mode 100644 index 0000000000..1baa60bcf2 --- /dev/null +++ b/include/interrupt.h @@ -0,0 +1,22 @@ +/* SPDX-License-Identifier: GPL-2.0-or-later */

+#include <asm/setjmp.h>

+/**

• • struct resume_data - data for resume after interrupt
• */

+struct resume_data {

•   /** @jump: longjmp buffer */
  

•   jmp_buf jump;
  

•   /** @code: exception code */
  

•   ulong code;
  

+};

+/**

• • set_resume() - set longjmp buffer for resuming after interrupt
• • When resuming the exception code will be returned in @data->code.
• • @data: pointer to structure with longjmp address
• */

+void set_resume(struct resume_data *data);

2.40.1