[LTP] [PATCH v3] ldt.h: Add workaround for x86_64

[Martin Doucha]

Hi,
safe_modify_ldt() should not allow any errors. Let's merge v2.

On 20. 05. 25 13:29, Ricardo B. Marlière wrote:
> From: Ricardo B. Marlière <rbm@suse.com>
> 
> The commit be0aaca2f742 ("syscalls/modify_ldt: Add lapi/ldt.h") left behind
> an important factor of modify_ldt(): the kernel intentionally casts the
> return value to unsigned int. This was handled in
> testcases/cve/cve-2015-3290.c but was removed. Add it back to the relevant
> file.
> 
> Reported-by: Martin Doucha <mdoucha@suse.cz>
> Reviewed-by: Martin Doucha <mdoucha@suse.cz>
> Signed-off-by: Ricardo B. Marlière <rbm@suse.com>
> ---
> Changes in v3:
> - EDITME: describe what is new in this series revision.
> - EDITME: use bulletpoints and terse descriptions.
> - Link to v2: https://lore.kernel.org/r/20250512-fixes-modify_ldt-v2-1-eaef5577e44e@suse.com
> 
> Changes in v2:
> - Added TBROK for any ret != 0 in modify_ldt call in cve-2015-3290.c
> - Link to v1: https://lore.kernel.org/r/20250507-fixes-modify_ldt-v1-1-70a2694cfddc@suse.com
> ---
>   include/lapi/ldt.h | 30 +++++++++++++++++++++++++++++-
>   1 file changed, 29 insertions(+), 1 deletion(-)
> 
> diff --git a/include/lapi/ldt.h b/include/lapi/ldt.h
> index 6b5a2d59cb41bfc24eb5ac26c3d47d49fb8ff78f..2533e50b9c02a974947c6628e9fa20c9c626aa34 100644
> --- a/include/lapi/ldt.h
> +++ b/include/lapi/ldt.h
> @@ -31,7 +31,27 @@ struct user_desc {
>   static inline int modify_ldt(int func, const struct user_desc *ptr,
>   			     unsigned long bytecount)
>   {
> -	return tst_syscall(__NR_modify_ldt, func, ptr, bytecount);
> +	long rval;
> +
> +	errno = 0;
> +	rval = tst_syscall(__NR_modify_ldt, func, ptr, bytecount);
> +
> +#ifdef __x86_64__
> +	/*
> +	 * The kernel intentionally casts modify_ldt() return value
> +	 * to unsigned int to prevent sign extension to 64 bits. This may
> +	 * result in syscall() returning the value as is instead of setting
> +	 * errno and returning -1.
> +	 */
> +	if (rval > 0 && (int)rval < 0) {
> +		tst_res(TINFO,
> +			"WARNING: Libc mishandled modify_ldt() return value");
> +		errno = -(int)errno;
> +		rval = -1;
> +	}
> +#endif /* __x86_64__ */
> +
> +	return rval;
>   }
>   
>   static inline int safe_modify_ldt(const char *file, const int lineno, int func,
> @@ -40,7 +60,15 @@ static inline int safe_modify_ldt(const char *file, const int lineno, int func,
>   {
>   	int rval;
>   
> +	errno = 0;
>   	rval = modify_ldt(func, ptr, bytecount);
> +#ifdef __x86_64__
> +	if (rval == -1 && errno == EINVAL) {
> +		tst_brk_(file, lineno, TCONF | TTERRNO,
> +			 "modify_ldt(%d, %p, %lu): 16-bit data segments are probably disabled",
> +			 func, ptr, bytecount);
> +	}
> +#endif
>   	if (rval == -1) {
>   		tst_brk_(file, lineno, TBROK | TERRNO,
>   			 "modify_ldt(%d, %p, %lu)", func, ptr, bytecount);
> 
> ---
> base-commit: b070a5692e035ec12c3d3c7a7e9e97c270fd4d7d
> change-id: 20250507-fixes-modify_ldt-ebcfdd2a7d30
> 
> Best regards,


-- 
Martin Doucha   mdoucha@suse.cz
SW Quality Engineer
SUSE LINUX, s.r.o.
CORSO IIa
Krizikova 148/34
186 00 Prague 8
Czech Republic