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AJvYcCUIc3q96vF+4vA9ZzEza4QMGP7FudiWQMPKTu2ZKkNbtNgPoaBcIKzqjlAXIB+ZyITbvqRMDrGFYQ==@kvack.org X-Gm-Message-State: AOJu0YyTUN5m6cqn2VLZBVEiGA/dHNg6Z0I1/izXs8yLFPRAlVYoNRec yzlVeq+he3wPg6cUXUzy/0ffahmTKriY1S+zrmFSmUhf9xnoEDHyyMnRRmRiYALYJSDBnDbqhJU cOMfWeP2MTrI0we80/tI0qucGNA4= X-Google-Smtp-Source: AGHT+IGt2176DfmuLWxLHRhUxP0ghtikgtAQtBs9a9ck/J1CfxjCxtNDV3zRVrMU5j3a8AABIjT1IH6bzLR1lWVcy+0= X-Received: by 2002:a05:6902:15c7:b0:e1d:1dee:eeeb with SMTP id 3f1490d57ef6-e1daff7cac4mr2967353276.22.1726256161483; Fri, 13 Sep 2024 12:36:01 -0700 (PDT) MIME-Version: 1.0 References: <20240912231650.3740732-1-debug@rivosinc.com> <20240912231650.3740732-22-debug@rivosinc.com> In-Reply-To: <20240912231650.3740732-22-debug@rivosinc.com> From: Andy Chiu Date: Fri, 13 Sep 2024 21:35:50 +0200 Message-ID: Subject: Re: [PATCH v4 21/30] riscv/traps: Introduce software check exception To: Deepak Gupta Cc: paul.walmsley@sifive.com, palmer@sifive.com, conor@kernel.org, linux-doc@vger.kernel.org, linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org, devicetree@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-arch@vger.kernel.org, linux-kselftest@vger.kernel.org, quic_zhonhan@quicinc.com, zong.li@sifive.com, zev@bewilderbeest.net, david@redhat.com, peterz@infradead.org, catalin.marinas@arm.com, broonie@kernel.org, dave.hansen@linux.intel.com, atishp@rivosinc.com, bjorn@rivosinc.com, namcaov@gmail.com, usama.anjum@collabora.com, guoren@kernel.org, alx@kernel.org, jszhang@kernel.org, hpa@zytor.com, puranjay@kernel.org, shuah@kernel.org, sorear@fastmail.com, costa.shul@redhat.com, robh@kernel.org, antonb@tenstorrent.com, quic_bjorande@quicinc.com, lorenzo.stoakes@oracle.com, corbet@lwn.net, dawei.li@shingroup.cn, anup@brainfault.org, deller@gmx.de, x86@kernel.org, andrii@kernel.org, willy@infradead.org, kees@kernel.org, mingo@redhat.com, libang.li@antgroup.com, samitolvanen@google.com, greentime.hu@sifive.com, osalvador@suse.de, ajones@ventanamicro.com, revest@chromium.org, ancientmodern4@gmail.com, aou@eecs.berkeley.edu, jerry.shih@sifive.com, alexghiti@rivosinc.com, arnd@arndb.de, yang.lee@linux.alibaba.com, charlie@rivosinc.com, bgray@linux.ibm.com, Liam.Howlett@oracle.com, leobras@redhat.com, songshuaishuai@tinylab.org, xiao.w.wang@intel.com, bp@alien8.de, cuiyunhui@bytedance.com, mchitale@ventanamicro.com, cleger@rivosinc.com, tglx@linutronix.de, krzk+dt@kernel.org, vbabka@suse.cz, brauner@kernel.org, bhe@redhat.com, ke.zhao@shingroup.cn, oleg@redhat.com, samuel.holland@sifive.com, ben.dooks@codethink.co.uk, evan@rivosinc.com, palmer@dabbelt.com, ebiederm@xmission.com, andy.chiu@sifive.com, schwab@suse.de, akpm@linux-foundation.org, sameo@rivosinc.com, tanzhasanwork@gmail.com, rppt@kernel.org, ryan.roberts@arm.com Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: A7EB1180010 X-Stat-Signature: q5t1x8rgbuhy5t8xegbj3393w6rbm4sr X-Rspam-User: X-HE-Tag: 1726256162-347978 X-HE-Meta: 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 7p07GDQZ 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Hi Deepak Deepak Gupta =E6=96=BC 2024=E5=B9=B49=E6=9C=8813=E6=97= =A5 =E9=80=B1=E4=BA=94 =E4=B8=8A=E5=8D=882:32=E5=AF=AB=E9=81=93=EF=BC=9A > > zicfiss / zicfilp introduces a new exception to priv isa `software check > exception` with cause code =3D 18. This patch implements software check > exception. > > Additionally it implements a cfi violation handler which checks for code > in xtval. If xtval=3D2, it means that sw check exception happened because= of > an indirect branch not landing on 4 byte aligned PC or not landing on > `lpad` instruction or label value embedded in `lpad` not matching label > value setup in `x7`. If xtval=3D3, it means that sw check exception happe= ned > because of mismatch between link register (x1 or x5) and top of shadow > stack (on execution of `sspopchk`). > > In case of cfi violation, SIGSEGV is raised with code=3DSEGV_CPERR. > SEGV_CPERR was introduced by x86 shadow stack patches. > > Signed-off-by: Deepak Gupta > --- > arch/riscv/include/asm/asm-prototypes.h | 1 + > arch/riscv/include/asm/entry-common.h | 2 ++ > arch/riscv/kernel/entry.S | 3 ++ > arch/riscv/kernel/traps.c | 38 +++++++++++++++++++++++++ > 4 files changed, 44 insertions(+) > > diff --git a/arch/riscv/include/asm/asm-prototypes.h b/arch/riscv/include= /asm/asm-prototypes.h > index cd627ec289f1..5a27cefd7805 100644 > --- a/arch/riscv/include/asm/asm-prototypes.h > +++ b/arch/riscv/include/asm/asm-prototypes.h > @@ -51,6 +51,7 @@ DECLARE_DO_ERROR_INFO(do_trap_ecall_u); > DECLARE_DO_ERROR_INFO(do_trap_ecall_s); > DECLARE_DO_ERROR_INFO(do_trap_ecall_m); > DECLARE_DO_ERROR_INFO(do_trap_break); > +DECLARE_DO_ERROR_INFO(do_trap_software_check); > > asmlinkage void handle_bad_stack(struct pt_regs *regs); > asmlinkage void do_page_fault(struct pt_regs *regs); > diff --git a/arch/riscv/include/asm/entry-common.h b/arch/riscv/include/a= sm/entry-common.h > index 2293e535f865..4068c7e5452a 100644 > --- a/arch/riscv/include/asm/entry-common.h > +++ b/arch/riscv/include/asm/entry-common.h > @@ -39,4 +39,6 @@ static inline int handle_misaligned_store(struct pt_reg= s *regs) > } > #endif > > +bool handle_user_cfi_violation(struct pt_regs *regs); > + > #endif /* _ASM_RISCV_ENTRY_COMMON_H */ > diff --git a/arch/riscv/kernel/entry.S b/arch/riscv/kernel/entry.S > index ca9203e6d76d..2ec75ba864a8 100644 > --- a/arch/riscv/kernel/entry.S > +++ b/arch/riscv/kernel/entry.S > @@ -384,6 +384,9 @@ SYM_DATA_START_LOCAL(excp_vect_table) > RISCV_PTR do_page_fault /* load page fault */ > RISCV_PTR do_trap_unknown > RISCV_PTR do_page_fault /* store page fault */ > + RISCV_PTR do_trap_unknown /* cause=3D16 */ > + RISCV_PTR do_trap_unknown /* cause=3D17 */ > + RISCV_PTR do_trap_software_check /* cause=3D18 is sw check except= ion */ > SYM_DATA_END_LABEL(excp_vect_table, SYM_L_LOCAL, excp_vect_table_end) > > #ifndef CONFIG_MMU > diff --git a/arch/riscv/kernel/traps.c b/arch/riscv/kernel/traps.c > index 51ebfd23e007..32d1453bed72 100644 > --- a/arch/riscv/kernel/traps.c > +++ b/arch/riscv/kernel/traps.c > @@ -354,6 +354,44 @@ void do_trap_ecall_u(struct pt_regs *regs) > > } > > +#define CFI_TVAL_FCFI_CODE 2 > +#define CFI_TVAL_BCFI_CODE 3 > +/* handle cfi violations */ > +bool handle_user_cfi_violation(struct pt_regs *regs) > +{ > + bool ret =3D false; > + unsigned long tval =3D csr_read(CSR_TVAL); > + > + if (((tval =3D=3D CFI_TVAL_FCFI_CODE) && cpu_supports_indirect_br= _lp_instr()) || > + ((tval =3D=3D CFI_TVAL_BCFI_CODE) && cpu_supports_shadow_= stack())) { > + do_trap_error(regs, SIGSEGV, SEGV_CPERR, regs->epc, > + "Oops - control flow violation"= ); > + ret =3D true; > + } > + > + return ret; > +} > +/* > + * software check exception is defined with risc-v cfi spec. Software ch= eck > + * exception is raised when:- > + * a) An indirect branch doesn't land on 4 byte aligned PC or `lpad` > + * instruction or `label` value programmed in `lpad` instr doesn't > + * match with value setup in `x7`. reported code in `xtval` is 2. > + * b) `sspopchk` instruction finds a mismatch between top of shadow stac= k (ssp) > + * and x1/x5. reported code in `xtval` is 3. > + */ It seems like this trap handler does not follow generic entry. This can cause problems as signal delivery is done in irqentry_exit_to_user_mode(). Please reference the commit f0bddf50586d ("riscv: entry: Convert to generic entry") for more information. > +asmlinkage __visible __trap_section void do_trap_software_check(struct p= t_regs *regs) > +{ > + if (user_mode(regs)) { > + /* not a cfi violation, then merge into flow of unknown t= rap handler */ > + if (!handle_user_cfi_violation(regs)) > + do_trap_unknown(regs); > + } else { > + /* sw check exception coming from kernel is a bug in kern= el */ > + die(regs, "Kernel BUG"); > + } > +} > + > #ifdef CONFIG_MMU > asmlinkage __visible noinstr void do_page_fault(struct pt_regs *regs) > { > -- > 2.45.0 > > > _______________________________________________ > linux-riscv mailing list > linux-riscv@lists.infradead.org > http://lists.infradead.org/mailman/listinfo/linux-riscv Cheers, Andy