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bh=tHJX+/j6dKMpSwR1pPR5+WZRefWjtKKPN5BWHqL2m04=; b=RWaKDtRhFipsb/IW9aOHcqkFQyQZNjobycHlu6Rvb3y9cjJWoHkE8c491kuoJq8Piuulnl oYH53dz3rMY2CyyclHx10OXZJgs79L9kzn76loWbM2LiGlLDZuBNSCJucNzf6AlpgQYxN1 0Pmg0t/6baxU/FrCYl8w9EulMwPm77s= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_ed25519; t=1782453249; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=tHJX+/j6dKMpSwR1pPR5+WZRefWjtKKPN5BWHqL2m04=; b=cK7I7wxosCY2Int1G05vwrQsWbcLuiwSUyWXaXsPpLEeLrx8gNqu3OmNeZfvZdpK5WcS81 GZqOIWo4aLK0P0BA== Date: Fri, 26 Jun 2026 07:54:08 +0200 From: Michal =?iso-8859-1?Q?Such=E1nek?= To: "Mukesh Kumar Chaurasiya (IBM)" Cc: maddy@linux.ibm.com, mpe@ellerman.id.au, npiggin@gmail.com, chleroy@kernel.org, sshegde@linux.ibm.com, mkchauras@linux.ibm.com, kees@kernel.org, mark.rutland@arm.com, ryan.roberts@arm.com, linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] powerpc/syscall: Fix seccomp errno handling with GENERIC_ENTRY Message-ID: References: <20260624171520.772408-1-mkchauras@gmail.com> X-Mailing-List: linuxppc-dev@lists.ozlabs.org List-Id: List-Help: List-Owner: List-Post: List-Archive: , List-Subscribe: , , List-Unsubscribe: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20260624171520.772408-1-mkchauras@gmail.com> X-Rspamd-Action: no action X-Rspamd-Server: rspamd2.dmz-prg2.suse.org X-Spamd-Result: default: False [2.49 / 50.00]; BAYES_HAM(-3.00)[100.00%]; HFILTER_HOSTNAME_UNKNOWN(2.50)[]; RDNS_NONE(2.00)[]; ONCE_RECEIVED(1.20)[]; HFILTER_HELO_IP_A(1.00)[kunlun.suse.cz]; NEURAL_HAM_LONG(-1.00)[-1.000]; HFILTER_HELO_NORES_A_OR_MX(0.30)[kunlun.suse.cz]; R_DKIM_ALLOW(-0.20)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; NEURAL_HAM_SHORT(-0.20)[-0.997]; MIME_GOOD(-0.10)[text/plain]; MX_GOOD(-0.01)[]; ARC_NA(0.00)[]; RCPT_COUNT_TWELVE(0.00)[12]; FUZZY_RATELIMITED(0.00)[rspamd.com]; MIME_TRACE(0.00)[0:+]; FREEMAIL_TO(0.00)[gmail.com]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; FREEMAIL_ENVRCPT(0.00)[gmail.com]; FREEMAIL_CC(0.00)[linux.ibm.com,ellerman.id.au,gmail.com,kernel.org,arm.com,lists.ozlabs.org,vger.kernel.org]; TO_DN_SOME(0.00)[]; FROM_EQ_ENVFROM(0.00)[]; FROM_HAS_DN(0.00)[]; TO_MATCH_ENVRCPT_ALL(0.00)[]; DNSWL_BLOCKED(0.00)[2a07:de40:b306:2000::2:from]; MISSING_XM_UA(0.00)[]; RCVD_COUNT_ZERO(0.00)[0]; DKIM_TRACE(0.00)[suse.de:+]; DBL_BLOCKED_OPENRESOLVER(0.00)[suse.de:email,suse.de:dkim] X-Spamd-Bar: ++ X-Rspamd-Queue-Id: 2A29A75BA2 Hello, On Wed, Jun 24, 2026 at 10:45:20PM +0530, Mukesh Kumar Chaurasiya (IBM) wrote: > After enabling GENERIC_ENTRY on PowerPC, seccomp filters using > SCMP_ACT_ERRNO without an explicit errnoRet value return ENOSYS > (Function not implemented) instead of the expected EPERM (Operation > not permitted). > > The issue occurs in system_call_exception() when syscall_enter_from_user_mode() > returns -1 to indicate the syscall should be skipped (e.g., blocked by seccomp). > The current code treats this -1 as a syscall number and compares it against > NR_syscalls. Since -1 (when cast to unsigned long) is greater than NR_syscalls, > the code incorrectly returns -ENOSYS, overwriting the errno that seccomp > already set via syscall_set_return_value(). > > The generic entry code in syscall_trace_enter() calls __secure_computing(), > which sets the appropriate errno in regs->gpr[3] and returns -1 to signal > that the syscall should be skipped. However, the PowerPC syscall handler > was not checking for this -1 return value before validating the syscall > number. > > Fix this by explicitly checking if syscall_enter_from_user_mode() returns > -1 and returning the value already set in regs->gpr[3] (the errno from > seccomp) before performing the syscall number validation. > > This aligns PowerPC's behavior with other architectures using GENERIC_ENTRY > and restores correct seccomp errno handling. > > Fixes: bee25f97ad24 ("powerpc: Enable GENERIC_ENTRY feature") > Reported-by: Michal Suchánek > Signed-off-by: Mukesh Kumar Chaurasiya (IBM) > --- > arch/powerpc/kernel/syscall.c | 4 ++++ > 1 file changed, 4 insertions(+) > > diff --git a/arch/powerpc/kernel/syscall.c b/arch/powerpc/kernel/syscall.c > index a9da2af6efa8..5b58c8d396c8 100644 > --- a/arch/powerpc/kernel/syscall.c > +++ b/arch/powerpc/kernel/syscall.c > @@ -22,6 +22,10 @@ notrace long system_call_exception(struct pt_regs *regs, unsigned long r0) > add_random_kstack_offset(); > r0 = syscall_enter_from_user_mode(regs, r0); > > + /* Seccomp or ptrace may have set return value, skip syscall */ > + if (unlikely(r0 == -1L)) > + return regs->gpr[3]; this should use syscall_get_error instead of accessing the register value directly. The error is represented differently in the scv and non-scv case, and for non-scv case this will return wrong value. Thanks Michal > + > if (unlikely(r0 >= NR_syscalls)) { > if (unlikely(trap_is_unsupported_scv(regs))) { > /* Unsupported scv vector */ > -- > 2.54.0 >