[PATCH v15 15/20] unwind_user: Flexible CFA recovery rules

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

To enable support for SFrame V3 flexible FDEs with a subsequent patch,
add support for the following flexible Canonical Frame Address (CFA)
recovery rules:

  CFA = SP + offset
  CFA = *(SP + offset)
  CFA = FP + offset
  CFA = *(FP + offset)
  CFA = register + offset
  CFA = *(register + offset)

Note that CFA recovery rules that use arbitrary register contents are
only valid when in the topmost frame, as their contents are otherwise
unknown.

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

Notes (jremus):
    Changes in v15:
    - enum unwind_user_cfa_rule, unwind_user_next_common(): Add support for
      SP/FP-based CFA recovery rules with dereferencing. (Sashiko AI)

 arch/x86/include/asm/unwind_user.h | 12 ++++++++----
 include/linux/unwind_user_types.h  | 22 ++++++++++++++++++++--
 kernel/unwind/sframe.c             | 15 +++++++++++++--
 kernel/unwind/user.c               | 24 ++++++++++++++++++++----
 4 files changed, 61 insertions(+), 12 deletions(-)

diff --git a/arch/x86/include/asm/unwind_user.h b/arch/x86/include/asm/unwind_user.h
index 9c3417be4283..f38f7c5ff1de 100644
--- a/arch/x86/include/asm/unwind_user.h
+++ b/arch/x86/include/asm/unwind_user.h
@@ -20,7 +20,10 @@ static inline int unwind_user_word_size(struct pt_regs *regs)
 #ifdef CONFIG_HAVE_UNWIND_USER_FP
 
 #define ARCH_INIT_USER_FP_FRAME(ws)			\
-	.cfa_off	=  2*(ws),			\
+	.cfa		= {				\
+		.rule		= UNWIND_USER_CFA_RULE_FP_OFFSET,\
+		.offset		=  2*(ws),		\
+			},				\
 	.ra		= {				\
 		.rule		= UNWIND_USER_RULE_CFA_OFFSET_DEREF,\
 		.offset		= -1*(ws),		\
@@ -29,11 +32,13 @@ static inline int unwind_user_word_size(struct pt_regs *regs)
 		.rule		= UNWIND_USER_RULE_CFA_OFFSET_DEREF,\
 		.offset		= -2*(ws),		\
 			},				\
-	.use_fp		= true,				\
 	.outermost	= false,
 
 #define ARCH_INIT_USER_FP_ENTRY_FRAME(ws)		\
-	.cfa_off	=  1*(ws),			\
+	.cfa		= {				\
+		.rule		= UNWIND_USER_CFA_RULE_SP_OFFSET,\
+		.offset		=  1*(ws),		\
+			},				\
 	.ra		= {				\
 		.rule		= UNWIND_USER_RULE_CFA_OFFSET_DEREF,\
 		.offset		= -1*(ws),		\
@@ -41,7 +46,6 @@ static inline int unwind_user_word_size(struct pt_regs *regs)
 	.fp		= {				\
 		.rule		= UNWIND_USER_RULE_RETAIN,\
 			},				\
-	.use_fp		= false,			\
 	.outermost	= false,
 
 static inline bool unwind_user_at_function_start(struct pt_regs *regs)
diff --git a/include/linux/unwind_user_types.h b/include/linux/unwind_user_types.h
index 0d02714a1b5d..c18be5b7d586 100644
--- a/include/linux/unwind_user_types.h
+++ b/include/linux/unwind_user_types.h
@@ -29,6 +29,25 @@ struct unwind_stacktrace {
 
 #define UNWIND_USER_RULE_DEREF			BIT(31)
 
+enum unwind_user_cfa_rule {
+	UNWIND_USER_CFA_RULE_SP_OFFSET,		/* CFA = SP + offset */
+	UNWIND_USER_CFA_RULE_FP_OFFSET,		/* CFA = FP + offset */
+	UNWIND_USER_CFA_RULE_REG_OFFSET,	/* CFA = register + offset */
+	/* DEREF variants */
+	UNWIND_USER_CFA_RULE_SP_OFFSET_DEREF =	/* CFA = *(SP + offset) */
+		UNWIND_USER_CFA_RULE_SP_OFFSET | UNWIND_USER_RULE_DEREF,
+	UNWIND_USER_CFA_RULE_FP_OFFSET_DEREF =	/* CFA = *(FP + offset) */
+		UNWIND_USER_CFA_RULE_FP_OFFSET | UNWIND_USER_RULE_DEREF,
+	UNWIND_USER_CFA_RULE_REG_OFFSET_DEREF =	/* CFA = *(register + offset) */
+		UNWIND_USER_CFA_RULE_REG_OFFSET | UNWIND_USER_RULE_DEREF,
+};
+
+struct unwind_user_cfa_rule_data {
+	enum unwind_user_cfa_rule rule;
+	s32 offset;
+	unsigned int regnum;
+};
+
 enum unwind_user_rule {
 	UNWIND_USER_RULE_RETAIN,		/* entity = entity */
 	UNWIND_USER_RULE_CFA_OFFSET,		/* entity = CFA + offset */
@@ -47,10 +66,9 @@ struct unwind_user_rule_data {
 };
 
 struct unwind_user_frame {
-	s32 cfa_off;
+	struct unwind_user_cfa_rule_data cfa;
 	struct unwind_user_rule_data ra;
 	struct unwind_user_rule_data fp;
-	bool use_fp;
 	bool outermost;
 };
 
diff --git a/kernel/unwind/sframe.c b/kernel/unwind/sframe.c
index e82d1dcdd471..6187379750db 100644
--- a/kernel/unwind/sframe.c
+++ b/kernel/unwind/sframe.c
@@ -283,6 +283,18 @@ static __always_inline int __read_fre(struct sframe_section *sec,
 	return -EFAULT;
 }
 
+static __always_inline void
+sframe_init_cfa_rule_data(struct unwind_user_cfa_rule_data *cfa_rule_data,
+			  unsigned char fre_info,
+			  s32 offset)
+{
+	if (SFRAME_V3_FRE_CFA_BASE_REG_ID(fre_info) == SFRAME_BASE_REG_FP)
+		cfa_rule_data->rule = UNWIND_USER_CFA_RULE_FP_OFFSET;
+	else
+		cfa_rule_data->rule = UNWIND_USER_CFA_RULE_SP_OFFSET;
+	cfa_rule_data->offset = offset;
+}
+
 static __always_inline void
 sframe_init_rule_data(struct unwind_user_rule_data *rule_data,
 		      s32 offset)
@@ -344,10 +356,9 @@ static __always_inline int __find_fre(struct sframe_section *sec,
 		return -EINVAL;
 	fre = prev_fre;
 
-	frame->cfa_off = fre->cfa_off;
+	sframe_init_cfa_rule_data(&frame->cfa, fre->info, fre->cfa_off);
 	sframe_init_rule_data(&frame->ra, fre->ra_off);
 	sframe_init_rule_data(&frame->fp, fre->fp_off);
-	frame->use_fp  = SFRAME_V3_FRE_CFA_BASE_REG_ID(fre->info) == SFRAME_BASE_REG_FP;
 	frame->outermost = SFRAME_V3_FRE_RA_UNDEFINED_P(fre->info);
 
 	return 0;
diff --git a/kernel/unwind/user.c b/kernel/unwind/user.c
index c6a2abac78e0..447061b10613 100644
--- a/kernel/unwind/user.c
+++ b/kernel/unwind/user.c
@@ -53,14 +53,30 @@ static int unwind_user_next_common(struct unwind_user_state *state,
 	}
 
 	/* Get the Canonical Frame Address (CFA) */
-	if (frame->use_fp) {
+	switch (frame->cfa.rule) {
+	case UNWIND_USER_CFA_RULE_SP_OFFSET:
+	case UNWIND_USER_CFA_RULE_SP_OFFSET_DEREF:
+		cfa = state->sp;
+		break;
+	case UNWIND_USER_CFA_RULE_FP_OFFSET:
+	case UNWIND_USER_CFA_RULE_FP_OFFSET_DEREF:
 		if (state->fp < state->sp)
 			return -EINVAL;
 		cfa = state->fp;
-	} else {
-		cfa = state->sp;
+		break;
+	case UNWIND_USER_CFA_RULE_REG_OFFSET:
+	case UNWIND_USER_CFA_RULE_REG_OFFSET_DEREF:
+		if (!state->topmost || unwind_user_get_reg(&cfa, frame->cfa.regnum))
+			return -EINVAL;
+		break;
+	default:
+		WARN_ON_ONCE(1);
+		return -EINVAL;
 	}
-	cfa += frame->cfa_off;
+	cfa += frame->cfa.offset;
+	if (frame->cfa.rule & UNWIND_USER_RULE_DEREF &&
+	    get_user_word(&cfa, cfa, 0, state->ws))
+		return -EINVAL;
 
 	/*
 	 * Make sure that stack is not going in wrong direction.  Allow SP
-- 
2.51.0