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Peter Anvin" , Mathieu Desnoyers , Kees Cook , Sam James Cc: Jens Remus , bpf@vger.kernel.org, linux-mm@kvack.org, Namhyung Kim , Andrii Nakryiko , "Jose E. Marchesi" , Beau Belgrave , Florian Weimer , "Carlos O'Donell" , Masami Hiramatsu , Jiri Olsa , Arnaldo Carvalho de Melo , Andrew Morton , David Hildenbrand , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Heiko Carstens , Vasily Gorbik , Ilya Leoshkevich Subject: [PATCH v14 14/19] unwind_user: Flexible FP/RA recovery rules Date: Tue, 5 May 2026 14:17:13 +0200 Message-ID: <20260505121718.3572346-15-jremus@linux.ibm.com> X-Mailer: git-send-email 2.51.0 In-Reply-To: <20260505121718.3572346-1-jremus@linux.ibm.com> References: <20260505121718.3572346-1-jremus@linux.ibm.com> Precedence: bulk X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Proofpoint-Reinject: loops=2 maxloops=12 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNTA1MDExNCBTYWx0ZWRfX0wRCLw1jLLWz WDXtsIOYA1bpJRM9NL7n9w+WuJE3fZ0sghrbhXA80rjVn+TJxwyDqef7Tj2AyE9LmEH2kVVRr47 aCMw4aKhUweeAvX3L/6rG3QJrLAhjiYdyaLCfjWtVXITRmbmY6eOChpe2qhQrUleIdn0abE+8Bk oqvin1EOSezmh3pjQrQmPm7dgYcBOHKlkzEjyKVTTQKMV2ucvLi2FbO+aFoKGfNdWsNdD9cziHM SGltGgqgvf9vqe8eBhaFlQHENvjhPFOzxvILcWosv1umy2zs2i8QMLI6N9KKFgfjTws5aBuU20Q NWGPFM5kRXNH71mPvHhUxCJ/xVIB3Q7p9O6gRO/3+lqqvdP3BPkJlDpmsSHIQ7xrIdn7MyP+bbH xww+Ingn9cAHByC3DSCisPcyvZJKxjspMdAbEitTn6VTm0pkFh6pE2PLBiS6+3508WRhVD5QaR8 lf1PpcLAH5eQoR6sFtw== X-Proofpoint-GUID: pnR1nFaxQUpyd1FpSrOluPbIAnOgGWMX X-Proofpoint-ORIG-GUID: YDladW5h7pO8Ko9AlmaJN6qgQyb2EtqC X-Authority-Analysis: v=2.4 cv=eu/vCIpX c=1 sm=1 tr=0 ts=69f9dfdd cx=c_pps a=5BHTudwdYE3Te8bg5FgnPg==:117 a=5BHTudwdYE3Te8bg5FgnPg==:17 a=NGcC8JguVDcA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=iQ6ETzBq9ecOQQE5vZCe:22 a=pGLkceISAAAA:8 a=VnNF1IyMAAAA:8 a=GjvnxKKRlEeFsqGDDKkA:9 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1143,Hydra:6.1.51,FMLib:17.12.100.49 definitions=2026-05-05_02,2026-04-30_02,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 phishscore=0 lowpriorityscore=0 clxscore=1015 adultscore=0 suspectscore=0 malwarescore=0 bulkscore=0 impostorscore=0 spamscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2604200000 definitions=main-2605050114 To enable support for SFrame V3 flexible FDEs with a subsequent patch, add support for the following flexible frame pointer (FP) and return address (RA) recovery rules: FP/RA = *(CFA + offset) FP/RA = register + offset FP/RA = *(register + offset) Note that FP/RA recovery rules that use arbitrary register contents are only valid when in the topmost frame, as their contents are otherwise unknown. This also enables unwinding of user space for architectures, such as s390, that may save the frame pointer (FP) and/or return address (RA) in other registers, for instance when in a leaf function. Reviewed-by: Indu Bhagat Signed-off-by: Jens Remus --- Notes (jremus): Changes in v14: - Improve comment on why UNWIND_USER_RULE_CFA_OFFSET is not implemented. (Mark Rutland) arch/x86/include/asm/unwind_user.h | 21 +++++++++--- include/linux/unwind_user.h | 9 +++++ include/linux/unwind_user_types.h | 23 +++++++++++-- kernel/unwind/sframe.c | 16 +++++++-- kernel/unwind/user.c | 53 ++++++++++++++++++++++++++---- 5 files changed, 107 insertions(+), 15 deletions(-) diff --git a/arch/x86/include/asm/unwind_user.h b/arch/x86/include/asm/unwind_user.h index 2dfb5ef11e36..9c3417be4283 100644 --- a/arch/x86/include/asm/unwind_user.h +++ b/arch/x86/include/asm/unwind_user.h @@ -21,15 +21,26 @@ static inline int unwind_user_word_size(struct pt_regs *regs) #define ARCH_INIT_USER_FP_FRAME(ws) \ .cfa_off = 2*(ws), \ - .ra_off = -1*(ws), \ - .fp_off = -2*(ws), \ + .ra = { \ + .rule = UNWIND_USER_RULE_CFA_OFFSET_DEREF,\ + .offset = -1*(ws), \ + }, \ + .fp = { \ + .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), \ - .ra_off = -1*(ws), \ - .fp_off = 0, \ + .ra = { \ + .rule = UNWIND_USER_RULE_CFA_OFFSET_DEREF,\ + .offset = -1*(ws), \ + }, \ + .fp = { \ + .rule = UNWIND_USER_RULE_RETAIN,\ + }, \ .use_fp = false, \ .outermost = false, @@ -41,4 +52,6 @@ static inline bool unwind_user_at_function_start(struct pt_regs *regs) #endif /* CONFIG_HAVE_UNWIND_USER_FP */ +#include + #endif /* _ASM_X86_UNWIND_USER_H */ diff --git a/include/linux/unwind_user.h b/include/linux/unwind_user.h index bc2edae39955..92cdf38c8ade 100644 --- a/include/linux/unwind_user.h +++ b/include/linux/unwind_user.h @@ -32,6 +32,15 @@ static inline int unwind_user_get_ra_reg(unsigned long *val) #define unwind_user_get_ra_reg unwind_user_get_ra_reg #endif +#ifndef unwind_user_get_reg +static inline int unwind_user_get_reg(unsigned long *val, unsigned int regnum) +{ + WARN_ON_ONCE(1); + return -EINVAL; +} +#define unwind_user_get_reg unwind_user_get_reg +#endif + int unwind_user(struct unwind_stacktrace *trace, unsigned int max_entries); #endif /* _LINUX_UNWIND_USER_H */ diff --git a/include/linux/unwind_user_types.h b/include/linux/unwind_user_types.h index 616cc5ee4586..0d02714a1b5d 100644 --- a/include/linux/unwind_user_types.h +++ b/include/linux/unwind_user_types.h @@ -27,10 +27,29 @@ struct unwind_stacktrace { unsigned long *entries; }; +#define UNWIND_USER_RULE_DEREF BIT(31) + +enum unwind_user_rule { + UNWIND_USER_RULE_RETAIN, /* entity = entity */ + UNWIND_USER_RULE_CFA_OFFSET, /* entity = CFA + offset */ + UNWIND_USER_RULE_REG_OFFSET, /* entity = register + offset */ + /* DEREF variants */ + UNWIND_USER_RULE_CFA_OFFSET_DEREF = /* entity = *(CFA + offset) */ + UNWIND_USER_RULE_CFA_OFFSET | UNWIND_USER_RULE_DEREF, + UNWIND_USER_RULE_REG_OFFSET_DEREF = /* entity = *(register + offset) */ + UNWIND_USER_RULE_REG_OFFSET | UNWIND_USER_RULE_DEREF, +}; + +struct unwind_user_rule_data { + enum unwind_user_rule rule; + s32 offset; + unsigned int regnum; +}; + struct unwind_user_frame { s32 cfa_off; - s32 ra_off; - s32 fp_off; + 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 d5e0fa04b99a..cc57804aa3b1 100644 --- a/kernel/unwind/sframe.c +++ b/kernel/unwind/sframe.c @@ -271,6 +271,18 @@ static __always_inline int __read_fre(struct sframe_section *sec, return -EFAULT; } +static __always_inline void +sframe_init_rule_data(struct unwind_user_rule_data *rule_data, + s32 offset) +{ + if (offset) { + rule_data->rule = UNWIND_USER_RULE_CFA_OFFSET_DEREF; + rule_data->offset = offset; + } else { + rule_data->rule = UNWIND_USER_RULE_RETAIN; + } +} + static __always_inline int __find_fre(struct sframe_section *sec, struct sframe_fde_internal *fde, unsigned long ip, @@ -321,8 +333,8 @@ static __always_inline int __find_fre(struct sframe_section *sec, fre = prev_fre; frame->cfa_off = fre->cfa_off; - frame->ra_off = fre->ra_off; - frame->fp_off = fre->fp_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); diff --git a/kernel/unwind/user.c b/kernel/unwind/user.c index 9ceef9b2b8db..89aecfbe3e84 100644 --- a/kernel/unwind/user.c +++ b/kernel/unwind/user.c @@ -61,22 +61,61 @@ static int unwind_user_next_common(struct unwind_user_state *state, return -EINVAL; /* Get the Return Address (RA) */ - if (frame->ra_off) { - if (get_user_word(&ra, cfa, frame->ra_off, state->ws)) - return -EINVAL; - } else { + switch (frame->ra.rule) { + case UNWIND_USER_RULE_RETAIN: if (!state->topmost || unwind_user_get_ra_reg(&ra)) return -EINVAL; + break; + /* + * UNWIND_USER_RULE_CFA_OFFSET doesn't make sense for RA. + * A return address cannot legitimately be a stack address. + */ + case UNWIND_USER_RULE_CFA_OFFSET_DEREF: + ra = cfa + frame->ra.offset; + break; + case UNWIND_USER_RULE_REG_OFFSET: + case UNWIND_USER_RULE_REG_OFFSET_DEREF: + if (!state->topmost || unwind_user_get_reg(&ra, frame->ra.regnum)) + return -EINVAL; + ra += frame->ra.offset; + break; + default: + WARN_ON_ONCE(1); + return -EINVAL; } + if (frame->ra.rule & UNWIND_USER_RULE_DEREF && + get_user_word(&ra, ra, 0, state->ws)) + return -EINVAL; /* Get the Frame Pointer (FP) */ - if (frame->fp_off && get_user_word(&fp, cfa, frame->fp_off, state->ws)) + switch (frame->fp.rule) { + case UNWIND_USER_RULE_RETAIN: + fp = state->fp; + break; + /* + * UNWIND_USER_RULE_CFA_OFFSET is currently not used for FP + * (e.g. SFrame cannot represent this rule). + */ + case UNWIND_USER_RULE_CFA_OFFSET_DEREF: + fp = cfa + frame->fp.offset; + break; + case UNWIND_USER_RULE_REG_OFFSET: + case UNWIND_USER_RULE_REG_OFFSET_DEREF: + if (!state->topmost || unwind_user_get_reg(&fp, frame->fp.regnum)) + return -EINVAL; + fp += frame->fp.offset; + break; + default: + WARN_ON_ONCE(1); + return -EINVAL; + } + if (frame->fp.rule & UNWIND_USER_RULE_DEREF && + get_user_word(&fp, fp, 0, state->ws)) return -EINVAL; state->ip = ra; state->sp = cfa; - if (frame->fp_off) - state->fp = fp; + state->fp = fp; state->topmost = false; return 0; } -- 2.51.0