Hi David,
Thanks for the update.
> -----Original Message-----
> x86_64_exception_frame() called with combined flags including
> EFRAME_VERIFY does not perform the verify. It's only done when
> EFRAME_VERIFY is the only flag set.
>
> Correct the condition to EFRAME_VERIFY if the flag is set. Verify
> requests are always performed. Fixes stack overrun "seek errors" seen on
> an x86_64 core when backtracing a PID at an IRQ stack where the
> interrupt handler doesn't save a pt_regs. Higher layers than the top
> frame on the IRQ stack were not displayed. Fixed by this change.
>
> But it breaks bt -e and bt -E for exceptions on userspace stacks. Those
> use the constant 0 as the kvaddr argument to x86_64_exception_frame()
> and pass the userspace stack position in the local argument.
> x86_64_exception_frame() only verifies the kvaddr argument. Zero is not
> accessible and EFRAME_VERIFY always fails for those cases.
>
> Modify the EFRAME_VERIFY block in x86_64_exception_frame() to choose
> kvaddr or local to verify using the same condition used to assign one of
> them to pt_regs_buf later in the same function. Add verify_addr to
> locals to hold the choice. Modify the accessible tests to use it instead
> of kvaddr. Type of the new variable is the same as the type of kvaddr.
>
> If verifying local argument, translate to a kernel address range using
> the stackbuf and stackbase members of the bt argument the same way used
> for EFRAME_SEARCH later in x86_64_exception_frame(). local and
> bt->stackbuf are char *, the assignment destination and bt->stackbase
> are ulong. Cast the char * variables to uintptr_t for the assignment
> arithmetic using the local argument to prevent gcc 10.2 errors assigning
> char * to ulong...the sum is okay without casts in the uses for function
> arguments later.
sorry for nitpicking, but I may need some study, what errors do you see?
If you replace uintptr_t with ulong, what do you see?
I cannot see any errors with Fedora gcc 10.2 without the casts.
and uintptr_t looks same as ulong. In the crash source code, we usually
use ulong for pointer value.
The patch logic looks good and tested OK.
Thanks,
Kazu
>
> Signed-off-by: David Mair <dmair@xxxxxxxx>
> ---
> diff --git a/x86_64.c b/x86_64.c
> index fc05e8a..9f4b5c7 100644
> --- a/x86_64.c
> +++ b/x86_64.c
> @@ -4412,15 +4412,20 @@ x86_64_exception_frame(ulong flags, ulong kvaddr, char *local,
> long r8, r9, r10, r11, r12, r13, r14, r15;
> struct machine_specific *ms;
> struct syment *sp;
> - ulong offset;
> + ulong offset, verify_addr;
> char *pt_regs_buf;
> long verified;
> long err;
> char buf[BUFSIZE];
>
> - if (flags == EFRAME_VERIFY) {
> - if (!accessible(kvaddr) ||
> - !accessible(kvaddr + SIZE(pt_regs) - sizeof(long)))
> + if (flags & EFRAME_VERIFY) {
> + if (kvaddr)
> + verify_addr = kvaddr;
> + else
> + verify_addr = ((uintptr_t)local - (uintptr_t)bt->stackbuf) + bt->stackbase;
> +
> + if (!accessible(verify_addr) ||
> + !accessible(verify_addr + SIZE(pt_regs) - sizeof(long)))
> return FALSE;
> }
>
>
> --
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