Re: [PATCH v14 12/19] unwind_user/sframe: Add .sframe validation option

[Jens Remus <jremus@linux.ibm.com>]

On 5/5/2026 2:17 PM, Jens Remus wrote:
> From: Josh Poimboeuf <jpoimboe@kernel.org>
> 
> Add a debug feature to validate all .sframe sections when first loading
> the file rather than on demand.
> 
> [ Jens Remus: Add support for SFrame V3.  Add support for PC-relative
> FDE function start offset.  Adjust to rename of struct sframe_fre to
> sframe_fre_internal.  Use %#x/%#lx format specifiers. ]

> diff --git a/kernel/unwind/sframe.c b/kernel/unwind/sframe.c

> +static int safe_read_fde(struct sframe_section *sec,
> +			 unsigned int fde_num, struct sframe_fde_internal *fde)
> +{
> +	int ret;
> +
> +	if (!user_read_access_begin((void __user *)sec->sframe_start,
> +				    sec->sframe_end - sec->sframe_start))
> +		return -EFAULT;
> +	ret = __read_fde(sec, fde_num, fde);
> +	user_read_access_end();
> +	return ret;
> +}

> +static int sframe_validate_section(struct sframe_section *sec)
> +{
> +	unsigned long prev_ip = 0;
> +	unsigned int i;
> +
> +	for (i = 0; i < sec->num_fdes; i++) {
> +		struct sframe_fre_internal *fre, *prev_fre = NULL;
> +		unsigned long ip, fre_addr;
> +		struct sframe_fde_internal fde;
> +		struct sframe_fre_internal fres[2];
> +		bool which = false;
> +		unsigned int j;
> +		int ret;
> +
> +		ret = safe_read_fde(sec, i, &fde);

Iterating over all FDEs may cause __read_fde() and thus safe_read_fde()
to fail if one sframe section covers multiple text sections (regardless
of whether it is also registered for multiple text sections), as
__read_fde() checks whether the read FDE function start address is
within [sec->text_start, sec->text_end[.

See my related comments in my reply to [PATCH v14 05/19] unwind_user/
sframe: Add support for reading .sframe contents.

> +		if (ret) {
> +			dbg_sec("safe_read_fde(%u) failed\n", i);
> +			return ret;
> +		}
> +
Regards,
Jens
-- 
Jens Remus
Linux on Z Development (D3303)
jremus@de.ibm.com / jremus@linux.ibm.com

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