On Tue, Oct 31, 2023 at 7:28 PM Jason Andryuk <jandr...@gmail.com> wrote:
>
> grub_gzio_read_real() uses grub_errno to identify decompression failures
> when the function completes. Its callees in gzio.c are void-returning
> functions that set grub_errno on their exit paths.
>
> A Fedora 38 machine was observed to fail `multiboot2 /xen.gz` with
> "premature end of file". xen.gz was well formed and could be
> successfully gunzip-ed in Linux.
>
> The TPM is flaky and produces errors when the verifier tries to extend
> PCRs with measurements. Logs show "Unkown TPM error" and grub_errno is
> set to GRUB_ERR_UNKNOWN_DEVICE. This pre-existing grub_errno causes an
> otherwise successful grub_gzio_read_real() call to return error.
This bus is likely to create other problems as well. Why not fix it?
If this error is meant to be ignored rather than stop loading, then it
should be discarded early, possibly printed. If it should stop loading
then this should really stop and not even get here
>
> Add a grub_debug_errno() macro to print existing grub_errno messages at
> the start of the function, and reset grub_errno to avoid such errors.
>
> Signed-off-by: Jason Andryuk <jandr...@gmail.com>
> ---
> v2:
> Add grub_debug_errno helper
> Separate debug from reset.
> ---
> grub-core/io/gzio.c | 4 ++++
> include/grub/err.h | 9 +++++++++
> 2 files changed, 13 insertions(+)
>
> diff --git a/grub-core/io/gzio.c b/grub-core/io/gzio.c
> index ca9355751..883df0011 100644
> --- a/grub-core/io/gzio.c
> +++ b/grub-core/io/gzio.c
> @@ -1294,6 +1294,10 @@ grub_gzio_read_real (grub_gzio_t gzio, grub_off_t
> offset,
> {
> grub_ssize_t ret = 0;
>
> + /* Avoid spurious failures on exit when grub_errno is already set. */
> + grub_debug_errno();
> + grub_errno = GRUB_ERR_NONE;
> +
> /* Do we reset decompression to the beginning of the file? */
> if (gzio->saved_offset > offset + WSIZE)
> initialize_tables (gzio);
> diff --git a/include/grub/err.h b/include/grub/err.h
> index 1c07034cd..f6948ecf8 100644
> --- a/include/grub/err.h
> +++ b/include/grub/err.h
> @@ -96,4 +96,13 @@ extern int EXPORT_VAR(grub_err_printed_errors);
> int grub_err_printf (const char *fmt, ...)
> __attribute__ ((format (GNU_PRINTF, 1, 2)));
>
> +#define grub_debug_errno() \
> +do { \
> + if ( grub_errno != GRUB_ERR_NONE ) \
> + { \
> + grub_dprintf ("errno", "%s: clearing pre-exising errmsg %s\n", \
> + __func__, grub_errmsg); \
> + } \
> +} while (0);
> +
> #endif /* ! GRUB_ERR_HEADER */
> --
> 2.41.0
>
>
> _______________________________________________
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> Grub-devel@gnu.org
> https://lists.gnu.org/mailman/listinfo/grub-devel
--
Regards
Vladimir 'phcoder' Serbinenko
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