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Peter Anvin" , Namhyung Kim , Andrii Nakryiko , Kees Cook , Sam James , Fangrui Song Subject: [RFC PATCH v2 20/24] unwind_user/eh_frame/x86: Handle PLT expressions Date: Fri, 21 Aug 2026 21:52:55 +0200 Message-ID: <20260821195259.2688377-21-jremus@linux.ibm.com> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260821195259.2688377-1-jremus@linux.ibm.com> References: <20260821195259.2688377-1-jremus@linux.ibm.com> Precedence: bulk X-Mailing-List: linux-s390@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-Info: AW1haW4tMjYwODIxMDE1NSBTYWx0ZWRfX8saOyv/gDEtr I7GxitEGxzBXqt1pRVMFNJZ4RmtOzWAeMZ+j6PmPFareRLK4ZFIr6J5+Dj9Cj+qfE2rV/DX+IJV tEbrIuaxINysFcTKQJnewbmwsbZi2PI= X-Proofpoint-GUID: 8Pcb3teDPGwBNila6rlEwAYe63BXY_49 X-Proofpoint-ORIG-GUID: YhFiri8BotwIrQ0cszGGj9zx1iESGqcp X-Authority-Analysis: v=2.4 cv=RPmD2Yi+ c=1 sm=1 tr=0 ts=6a88acb3 cx=c_pps a=aDMHemPKRhS1OARIsFnwRA==:117 a=aDMHemPKRhS1OARIsFnwRA==:17 a=Sv0fKeRqtYgA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=Y2IxJ9c9Rs8Kov3niI8_:22 a=VnNF1IyMAAAA:8 a=lN3RThuQUzBg4E8S6xQA:9 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwODIxMDE1NSBTYWx0ZWRfXxTMwDFTKXbZm pGZh2l9Z7VR4zY+X/cgKMfpT4fNO78LDpTFCBxiaOAQdhFR5sSKTx6QvwcWMq0BpcaDEbX3m/DC w+mBr6FWnoY6yji98ZU/dI0S6itM5NbJzPP0ZMzHJSuy1LCsrSXhxwULnDfvt+rSkqKjXLXCNbt TsJYkfgg25wAw2YcBR+NYJ8EqVLYErLvQn6zQbeWIe5bGFLVaG5oWHHAQyEr24hID6eRCVayuYc lLAjkvxRhEforXMgyIjojcUyzh8r31cDQaI59nDNno4o6R+QoDpyx3N5VGyszBso71RcpGHY5hu S/t5o2QYHzYZRIgIcG1Bjo7EwH7TvErx5d7JfwWX6AsF85QW0MmlYPCVsA6ItTPmwSF79C5aG94 oFuek4rl0KgmKGDHUZvAYwW0RbubhBQtxL4qfp4X3H/8TBm4R6kqT+fA4pjnpWOa+yMWt9ikBUo LDIYUoMRiKLyCN4ntdg== X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1176,Hydra:6.1.134,FMLib:17.12.100.49 definitions=2026-08-21_06,2026-08-21_02,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 clxscore=1015 phishscore=0 adultscore=0 spamscore=0 priorityscore=1501 bulkscore=0 impostorscore=0 malwarescore=0 lowpriorityscore=0 suspectscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2606150000 definitions=main-2608210155 Add x86-specific support for handling the CFA expression found in GNU linker generated .eh_frame for PLT. This enables unwinding through GNU linker generated PLT entries on i386 and x86-64, unless linker option --no-ld-generated-unwind-info is used. Signed-off-by: Jens Remus --- arch/x86/include/asm/unwind_user_eh_frame.h | 68 ++++++++++++++++++++- kernel/unwind/eh_frame.c | 3 +- kernel/unwind/eh_frame.h | 14 +++++ 3 files changed, 83 insertions(+), 2 deletions(-) diff --git a/arch/x86/include/asm/unwind_user_eh_frame.h b/arch/x86/include/asm/unwind_user_eh_frame.h index fdccbda2fe4b..8268eb1a0ff5 100644 --- a/arch/x86/include/asm/unwind_user_eh_frame.h +++ b/arch/x86/include/asm/unwind_user_eh_frame.h @@ -2,6 +2,8 @@ #ifndef _ASM_X86_UNWIND_USER_EH_FRAME_H #define _ASM_X86_UNWIND_USER_EH_FRAME_H +#include + #ifdef CONFIG_X86_64 #define EH_FRAME_REG_SP 7 /* designated stack pointer register */ @@ -15,7 +17,71 @@ #define EH_FRAME_MIN_DATA_ALIGN -8 #define EH_FRAME_MAX_DATA_ALIGN -1 -#endif +#endif /* CONFIG_X86_64 */ + +static inline int memcmp_masked(const void *s1, const void *s2, + const void *mask, size_t n) +{ + const unsigned char *p1 = s1, *p2 = s2, *m = mask; + int res = 0; + + while (n--) + if ((res = (*p1++ ^ *p2++) & *m++)) + break; + + return res; +} + +static inline int eh_frame_do_def_cfa_expression(const char *expr, + int size, + unsigned long ip, + struct eh_frame_reg_state *reg_state) +{ + /* + * PLT CFA expression: + * + * DW_OP_breg + // 4 (ESP) + 4 or 7 (RSP) + 8 + * DW_OP_breg + 0 // 8 (EIP) or 16 (RIP) + * DW_OP_lit15 + * DW_OP_and + * DW_OP_lit + * DW_OP_ge + * DW_OP_lit // 2 or 3 + * DW_OP_shl + * DW_OP_plus + * + * CFA = (SP + offset) + (((IP & 0xf) >= N) << shift) + */ + static const char plt_expr[] = {0x00,0x00,0x00,0x00,0x3f,0x1a,0x30,0x2a,0x30,0x24,0x22}; + static const char plt_mask[] = {0x00,0xf0,0x00,0xff,0xff,0xff,0xf0,0xff,0xf0,0xff,0xff}; + + if (size == sizeof(plt_expr) && + !memcmp_masked(expr, plt_expr, plt_mask, sizeof(plt_expr))) { + unsigned char sp_op = expr[0]; + unsigned char sp_offset = expr[1] & 0x0f; + unsigned char ip_op = expr[2]; + unsigned char n = DW_OP_lit_value(expr[6]); + unsigned char shift = DW_OP_lit_value(expr[8]); + unsigned char sp_reg, ip_reg; + + if (!DW_OP_is_breg(sp_op) || !DW_OP_is_breg(ip_op)) + return -EOPNOTSUPP; + + sp_reg = DW_OP_breg_register(sp_op); + ip_reg = DW_OP_breg_register(ip_op); + if (sp_reg != EH_FRAME_REG_SP || ip_reg != EH_FRAME_REG_RA) + return -EOPNOTSUPP; + + /* CFA = (SP + SP_offset) + (((IP & 0xf) >= N) << shift) */ + reg_state->cfa_rule = CFA_REG_OFFSET; + reg_state->cfa_regnum = EH_FRAME_REG_SP; + reg_state->cfa_offset = sp_offset + (((ip & 15) >= n) << shift); + return 0; + } + + return -EOPNOTSUPP; +} +#define eh_frame_do_def_cfa_expression eh_frame_do_def_cfa_expression #include diff --git a/kernel/unwind/eh_frame.c b/kernel/unwind/eh_frame.c index a98804dbe588..0a81ba1a0377 100644 --- a/kernel/unwind/eh_frame.c +++ b/kernel/unwind/eh_frame.c @@ -15,11 +15,12 @@ #include #include #include -#include #include "eh_frame.h" #include "eh_frame_debug.h" +#include + struct eh_frame_cfi_context { struct eh_frame_reg_state state; struct eh_frame_reg_state stack[EH_FRAME_MAX_STATE_STACK]; diff --git a/kernel/unwind/eh_frame.h b/kernel/unwind/eh_frame.h index a43560486283..2f87d1b32bbc 100644 --- a/kernel/unwind/eh_frame.h +++ b/kernel/unwind/eh_frame.h @@ -60,6 +60,20 @@ #define DW_EH_PE_format(encoding) ((encoding) & 0x0f) #define DW_EH_PE_application(encoding) ((encoding) & 0x70) +/* DWARF expression operations */ +#define DW_OP_lit0 0x30 +/* ... */ +#define DW_OP_lit31 0x4f +#define DW_OP_breg0 0x70 +/* ... */ +#define DW_OP_breg31 0x8f + +/* Helpers for DWARF expression operations */ +#define DW_OP_is_lit(op) ((op) >= DW_OP_lit0 && (op) <= DW_OP_lit31) +#define DW_OP_is_breg(op) ((op) >= DW_OP_breg0 && (op) <= DW_OP_breg31) +#define DW_OP_lit_value(op) ((op) - DW_OP_lit0) +#define DW_OP_breg_register(op) ((op) - DW_OP_breg0) + /* CIE/FDE constants */ #define EH_FRAME_CIE_ID 0 #define EH_FRAME_DWARF64_LENGTH 0xffffffff -- 2.53.0