[RFC PATCH v1 05/25] unwind_user: Flexible CFA recovery rules
From: Jens Remus
Date: Tue Aug 18 2026 - 10:53:48 EST
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@xxxxxxxxx>
Signed-off-by: Jens Remus <jremus@xxxxxxxxxxxxx>
---
Notes (jremus):
Cherry-picked from "[PATCH v16 00/20] unwind_deferred: Implement sframe
handling" series:
https://lore.kernel.org/all/20260521142546.3908498-16-jremus@xxxxxxxxxxxxx/
arch/x86/include/asm/unwind_user.h | 12 ++++++++----
include/linux/unwind_user_types.h | 22 ++++++++++++++++++++--
kernel/unwind/user.c | 24 ++++++++++++++++++++----
3 files changed, 48 insertions(+), 10 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 1b5db76e886a..670ac860ae76 100644
--- a/include/linux/unwind_user_types.h
+++ b/include/linux/unwind_user_types.h
@@ -27,6 +27,25 @@ 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 */
@@ -45,10 +64,9 @@ 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/user.c b/kernel/unwind/user.c
index f5d68e86d72b..9df5040df9b3 100644
--- a/kernel/unwind/user.c
+++ b/kernel/unwind/user.c
@@ -52,14 +52,30 @@ 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
--
2.53.0