Re: [PATCH v3 09/19] unwind: Introduce sframe user space unwinding

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

On 28.10.2024 22:47, Josh Poimboeuf wrote:
...

> diff --git a/kernel/unwind/sframe.c b/kernel/unwind/sframe.c
...
> +#define __SFRAME_GET_USER(out, user_ptr, type)				\
> +({									\
> +	type __tmp;							\
> +	if (get_user(__tmp, (type __user *)user_ptr))			\
> +		return -EFAULT;						\
> +	user_ptr += sizeof(__tmp);					\
> +	out = __tmp;							\
> +})
> +
> +#define SFRAME_GET_USER(out, user_ptr, size)				\
> +({									\
> +	switch (size) {							\
> +	case 1:								\
> +		__SFRAME_GET_USER(out, user_ptr, u8);			\
> +		break;							\
> +	case 2:								\
> +		__SFRAME_GET_USER(out, user_ptr, u16);			\
> +		break;							\
> +	case 4:								\
> +		__SFRAME_GET_USER(out, user_ptr, u32);			\
> +		break;							\
> +	default:							\
> +		return -EINVAL;						\
> +	}								\
> +})
> +
> +static unsigned char fre_type_to_size(unsigned char fre_type)
> +{
> +	if (fre_type > 2)
> +		return 0;
> +	return 1 << fre_type;
> +}
> +
> +static unsigned char offset_size_enum_to_size(unsigned char off_size)
> +{
> +	if (off_size > 2)
> +		return 0;
> +	return 1 << off_size;
> +}
...
> +static int find_fre(struct sframe_section *sec, struct sframe_fde *fde,
> +		    unsigned long ip, struct unwind_user_frame *frame)
> +{
> +	unsigned char fde_type = SFRAME_FUNC_FDE_TYPE(fde->info);
> +	unsigned char fre_type = SFRAME_FUNC_FRE_TYPE(fde->info);
> +	unsigned char offset_count, offset_size;
> +	s32 cfa_off, ra_off, fp_off, ip_off;
> +	void __user *f, *last_f = NULL;
> +	unsigned char addr_size;
> +	u32 last_fre_ip_off = 0;
> +	u8 fre_info = 0;
> +	int i;
> +
> +	addr_size = fre_type_to_size(fre_type);
> +	if (!addr_size)
> +		return -EINVAL;
> +
> +	ip_off = ip - (sec->sframe_addr + fde->start_addr);
> +
> +	f = (void __user *)sec->fres_addr + fde->fres_off;
> +
> +	for (i = 0; i < fde->fres_num; i++) {
> +		u32 fre_ip_off;
> +
> +		SFRAME_GET_USER(fre_ip_off, f, addr_size);
> +
> +		if (fre_ip_off < last_fre_ip_off)
> +			return -EINVAL;
> +
> +		last_fre_ip_off = fre_ip_off;
> +
> +		if (fde_type == SFRAME_FDE_TYPE_PCINC) {
> +			if (ip_off < fre_ip_off)
> +				break;
> +		} else {
> +			/* SFRAME_FDE_TYPE_PCMASK */
> +			if (ip_off % fde->rep_size < fre_ip_off)
> +				break;
> +		}
> +
> +		SFRAME_GET_USER(fre_info, f, 1);
> +
> +		offset_count = SFRAME_FRE_OFFSET_COUNT(fre_info);
> +		offset_size  = offset_size_enum_to_size(SFRAME_FRE_OFFSET_SIZE(fre_info));
> +
> +		if (!offset_count || !offset_size)
> +			return -EINVAL;
> +
> +		last_f = f;
> +		f += offset_count * offset_size;
> +	}
> +
> +	if (!last_f)
> +		return -EINVAL;
> +
> +	f = last_f;
> +
> +	SFRAME_GET_USER(cfa_off, f, offset_size);

SFRAME_GET_USER() does not work for the signed SFrame CFA offset.

> +	offset_count--;
> +
> +	ra_off = sec->ra_off;
> +	if (!ra_off) {
> +		if (!offset_count--)
> +			return -EINVAL;
> +
> +		SFRAME_GET_USER(ra_off, f, offset_size);

Likewise for the signed SFrame RA offset.

Excerpt from my added trace. Note the RA_off=65488 (unsigned) = 0xFFD0 = 
-48 (signed):

unwind_user_next: WARNING: RA could not be obtained from user space 
(IP=0x000003ffbb5f4218, CFA=0x000003ffc22f8f10, RA_off=65488)

Excerpt from perf script:

3ffbb5f4218 internal_fnwmatch+0x558 (/usr/lib64/libc.so.6)

Excerpts from objdump -wt --sframe:

00000000000f3cc0 l     F .text  000000000000195c 
internal_fnwmatch

func idx [1715]: pc = 0xf3cc0, size = 6492 bytes
STARTPC         CFA       FP        RA           INFO
00000000000f3cc0  sp+160    u         u            (1*1B)
00000000000f3cc6  sp+160    c-72      c-48         (3*1B)
00000000000f3cd0  sp+4256   c-72      c-48         (3*2B)
00000000000f3cdc  sp+8352   c-72      c-48         (3*2B)
00000000000f3ce8  sp+10792  c-72      c-48         (3*2B)
00000000000f3f7e  sp+160    u         u            (1*1B)
00000000000f3f80  sp+10792  c-72      c-48         (3*2B)

> +	}
> +
> +	fp_off = sec->fp_off;
> +	if (!fp_off && offset_count) {
> +		offset_count--;
> +		SFRAME_GET_USER(fp_off, f, offset_size);

Likewise for the signed SFrame FP offset.

> +	}
> +
> +	if (offset_count)
> +		return -EINVAL;
> +
> +	frame->cfa_off = cfa_off;
> +	frame->ra_off = ra_off;
> +	frame->fp_off = fp_off;
> +	frame->use_fp = SFRAME_FRE_CFA_BASE_REG_ID(fre_info) == SFRAME_BASE_REG_FP;
> +
> +	return 0;
> +}
...

I have verified that reintroducing and using SFRAME_GET_USER_SIGNED() 
works correctly.

Regards,
Jens
-- 
Jens Remus
Linux on Z Development (D3303) and z/VSE Support
+49-7031-16-1128 Office
jremus@de.ibm.com

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