[PATCH v14 17/19] unwind_user/sframe: Separate reading of FRE from reading of FRE data words

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

__find_fre() performs linear search for a matching SFrame FRE for a
given IP.  For that purpose it uses __read_fre(), which reads the whole
FRE.  That is the variable-size FRE structure as well as the trailing
variable-length array of variable-size data words.  For the search logic
to skip over the FRE it would be sufficient to read the variable-size
FRE structure only, which includes the count and size of data words.

Add fields to struct sframe_fre_internal to store the FRE data word's
address, count, and size.  Change __read_fre() to read the variable-
size FRE structure only and populate those new fields.  Change
__read_fre_datawords() to use those new fields.  Change __find_fre()
to use __read_fre_datawords() to read the FRE data words only after a
matching FRE has been found.  Introduce safe_read_fre_datawords() and
use it in sframe_validate_section() to validate that the FRE data words.

Reviewed-by: Indu Bhagat <ibhagatgnu@gmail.com>
Signed-off-by: Jens Remus <jremus@linux.ibm.com>
---

Notes (jremus):
    Changes in v14:
    - Adjust to rename of SFRAME_FDE_TYPE_* and
      __read_default_fre_datawords().
    - Update function name in debug message.

 kernel/unwind/sframe.c | 91 +++++++++++++++++++++++++++---------------
 1 file changed, 58 insertions(+), 33 deletions(-)

diff --git a/kernel/unwind/sframe.c b/kernel/unwind/sframe.c
index 2ba2c8b385f9..98346412078b 100644
--- a/kernel/unwind/sframe.c
+++ b/kernel/unwind/sframe.c
@@ -39,6 +39,9 @@ struct sframe_fre_internal {
 	u32		fp_ctl;
 	s32		fp_off;
 	u8		info;
+	unsigned long	dw_addr;
+	unsigned char	dw_count;
+	unsigned char	dw_size;
 };
 
 DEFINE_STATIC_SRCU(sframe_srcu);
@@ -196,11 +199,11 @@ static __always_inline int __find_fde(struct sframe_section *sec,
 static __always_inline int
 __read_default_fre_datawords(struct sframe_section *sec,
 			     struct sframe_fde_internal *fde,
-			     unsigned long cur,
-			     unsigned char dataword_count,
-			     unsigned char dataword_size,
 			     struct sframe_fre_internal *fre)
 {
+	unsigned char dataword_count = fre->dw_count;
+	unsigned char dataword_size = fre->dw_size;
+	unsigned long cur = fre->dw_addr;
 	s32 cfa_off, ra_off, fp_off;
 	unsigned int cfa_regnum;
 
@@ -242,11 +245,11 @@ __read_default_fre_datawords(struct sframe_section *sec,
 static __always_inline int
 __read_flex_fde_fre_datawords(struct sframe_section *sec,
 			      struct sframe_fde_internal *fde,
-			      unsigned long cur,
-			      unsigned char dataword_count,
-			      unsigned char dataword_size,
 			      struct sframe_fre_internal *fre)
 {
+	unsigned char dataword_count = fre->dw_count;
+	unsigned char dataword_size = fre->dw_size;
+	unsigned long cur = fre->dw_addr;
 	u32 cfa_ctl, ra_ctl, fp_ctl;
 	s32 cfa_off, ra_off, fp_off;
 
@@ -303,24 +306,28 @@ __read_flex_fde_fre_datawords(struct sframe_section *sec,
 static __always_inline int
 __read_fre_datawords(struct sframe_section *sec,
 		     struct sframe_fde_internal *fde,
-		     unsigned long cur,
-		     unsigned char dataword_count,
-		     unsigned char dataword_size,
 		     struct sframe_fre_internal *fre)
 {
 	unsigned char fde_type = SFRAME_V3_FDE_TYPE(fde->info2);
+	unsigned char dataword_count = fre->dw_count;
+
+	if (!dataword_count) {
+		/* A FRE without data words indicates an outermost frame. */
+		fre->cfa_ctl	= 0;
+		fre->cfa_off	= 0;
+		fre->ra_ctl	= 0;
+		fre->ra_off	= 0;
+		fre->fp_ctl	= 0;
+		fre->fp_off	= 0;
+
+		return 0;
+	}
 
 	switch (fde_type) {
 	case SFRAME_FDE_TYPE_DEFAULT:
-		return __read_default_fre_datawords(sec, fde, cur,
-						    dataword_count,
-						    dataword_size,
-						    fre);
+		return __read_default_fre_datawords(sec, fde, fre);
 	case SFRAME_FDE_TYPE_FLEX:
-		return __read_flex_fde_fre_datawords(sec, fde, cur,
-						     dataword_count,
-						     dataword_size,
-						     fre);
+		return __read_flex_fde_fre_datawords(sec, fde, fre);
 	default:
 		return -EFAULT;
 	}
@@ -362,23 +369,11 @@ static __always_inline int __read_fre(struct sframe_section *sec,
 	fre->size	= addr_size + 1 + (dataword_count * dataword_size);
 	fre->ip_off	= ip_off;
 	fre->info	= info;
+	fre->dw_addr	= cur;
+	fre->dw_count	= dataword_count;
+	fre->dw_size	= dataword_size;
 
-	if (!dataword_count) {
-		/*
-		 * A FRE without data words indicates RA undefined /
-		 * outermost frame.
-		 */
-		fre->cfa_ctl	= 0;
-		fre->cfa_off	= 0;
-		fre->ra_ctl	= 0;
-		fre->ra_off	= 0;
-		fre->fp_ctl	= 0;
-		fre->fp_off	= 0;
-
-		return 0;
-	}
-
-	return __read_fre_datawords(sec, fde, cur, dataword_count, dataword_size, fre);
+	return 0;
 
 Efault:
 	return -EFAULT;
@@ -455,6 +450,7 @@ static __always_inline int __find_fre(struct sframe_section *sec,
 	bool which = false;
 	unsigned int i;
 	u32 ip_off;
+	int ret;
 
 	ip_off = ip - fde->func_addr;
 
@@ -492,6 +488,10 @@ static __always_inline int __find_fre(struct sframe_section *sec,
 		return -EINVAL;
 	fre = prev_fre;
 
+	ret = __read_fre_datawords(sec, fde, fre);
+	if (ret)
+		return ret;
+
 	if (sframe_init_cfa_rule_data(&frame->cfa, fre->cfa_ctl, fre->cfa_off))
 		return -EINVAL;
 	sframe_init_rule_data(&frame->ra, fre->ra_ctl, fre->ra_off);
@@ -567,6 +567,20 @@ static int safe_read_fre(struct sframe_section *sec,
 	return ret;
 }
 
+static int safe_read_fre_datawords(struct sframe_section *sec,
+				   struct sframe_fde_internal *fde,
+				   struct sframe_fre_internal *fre)
+{
+	int ret;
+
+	if (!user_read_access_begin((void __user *)sec->sframe_start,
+				    sec->sframe_end - sec->sframe_start))
+		return -EFAULT;
+	ret = __read_fre_datawords(sec, fde, fre);
+	user_read_access_end();
+	return ret;
+}
+
 static int sframe_validate_section(struct sframe_section *sec)
 {
 	unsigned long prev_ip = 0;
@@ -612,6 +626,17 @@ static int sframe_validate_section(struct sframe_section *sec)
 					fde.rep_size);
 				return ret;
 			}
+			ret = safe_read_fre_datawords(sec, &fde, fre);
+			if (ret) {
+				dbg_sec("FDE %u: safe_read_fre_datawords(%u) failed\n", i, j);
+				dbg_sec("FDE: func_addr:%#lx func_size:%#x fda_off:%#x fres_off:%#x fres_num:%d info:%u info2:%u rep_size:%u\n",
+					fde.func_addr, fde.func_size,
+					fde.fda_off,
+					fde.fres_off, fde.fres_num,
+					fde.info, fde.info2,
+					fde.rep_size);
+				return ret;
+			}
 
 			fre_addr += fre->size;
 
-- 
2.51.0