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Tue, 24 Feb 2026 09:49:51 -0800 (PST) Received: from draig.lan ([185.124.0.126]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-b9084cad8ebsm445252066b.27.2026.02.24.09.49.49 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 24 Feb 2026 09:49:49 -0800 (PST) Received: from draig (localhost [IPv6:::1]) by draig.lan (Postfix) with ESMTP id E4EEB5F7B4; Tue, 24 Feb 2026 17:49:48 +0000 (GMT) From: =?utf-8?Q?Alex_Benn=C3=A9e?= To: Florian Hofhammer Cc: qemu-devel@nongnu.org, pierrick.bouvier@linaro.org, richard.henderson@linaro.org, laurent@vivier.eu, imp@bsdimp.com, berrange@redhat.com Subject: Re: [PATCH v4 6/7] plugins: prohibit writing to read-only registers In-Reply-To: (Florian Hofhammer's message of "Tue, 24 Feb 2026 16:57:21 +0100") References: <909b0a4f-9759-4e27-bba8-997ae2f41bd6@epfl.ch> User-Agent: mu4e 1.14.0-pre1; emacs 30.1 Date: Tue, 24 Feb 2026 17:49:48 +0000 Message-ID: <87ldgi2fr7.fsf@draig.linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Received-SPF: pass client-ip=2a00:1450:4864:20::62b; envelope-from=alex.bennee@linaro.org; helo=mail-ej1-x62b.google.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: qemu development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Florian Hofhammer writes: > The opaque register handle encodes whether a register is read-only in > the lowest bit and prevents writing to the register via the plugin API > in this case. > > Signed-off-by: Florian Hofhammer > --- > plugins/api.c | 11 +++++++---- > 1 file changed, 7 insertions(+), 4 deletions(-) > > diff --git a/plugins/api.c b/plugins/api.c > index b2c52d2a09..3a8479ddce 100644 > --- a/plugins/api.c > +++ b/plugins/api.c > @@ -424,6 +424,7 @@ static GArray *create_register_handles(GArray *gdbstu= b_regs) > for (int i =3D 0; i < gdbstub_regs->len; i++) { > GDBRegDesc *grd =3D &g_array_index(gdbstub_regs, GDBRegDesc, i); > qemu_plugin_reg_descriptor desc; > + gint plugin_ro_bit =3D 0; >=20=20 > /* skip "un-named" regs */ > if (!grd->name) { > @@ -431,7 +432,6 @@ static GArray *create_register_handles(GArray *gdbstu= b_regs) > } >=20=20 > /* Create a record for the plugin */ > - desc.handle =3D GINT_TO_POINTER(grd->gdb_reg + 1); > desc.name =3D g_intern_string(grd->name); > desc.is_readonly =3D false; > if (g_strcmp0(desc.name, pc_str) =3D=3D 0 > @@ -442,7 +442,9 @@ static GArray *create_register_handles(GArray *gdbstu= b_regs) > || g_strcmp0(desc.name, rpc_str) =3D=3D 0 > ) { > desc.is_readonly =3D true; > + plugin_ro_bit =3D 1; > } > + desc.handle =3D GINT_TO_POINTER((grd->gdb_reg << 1) | plugin_ro_= bit); > desc.feature =3D g_intern_string(grd->feature_name); > g_array_append_val(find_data, desc); > } > @@ -467,7 +469,7 @@ bool qemu_plugin_read_register(struct qemu_plugin_reg= ister *reg, > return false; > } >=20=20 > - return (gdb_read_register(current_cpu, buf, GPOINTER_TO_INT(reg) - 1= ) > 0); > + return (gdb_read_register(current_cpu, buf, GPOINTER_TO_INT(reg) >> = 1) > 0); > } >=20=20 > bool qemu_plugin_write_register(struct qemu_plugin_register *reg, > @@ -476,11 +478,12 @@ bool qemu_plugin_write_register(struct qemu_plugin_= register *reg, > g_assert(current_cpu); >=20=20 > if (buf->len =3D=3D 0 || (qemu_plugin_get_cb_flags() !=3D QEMU_PLUGI= N_CB_RW_REGS && > - qemu_plugin_get_cb_flags() !=3D QEMU_PLUGIN_CB= _RW_REGS_PC)) { > + qemu_plugin_get_cb_flags() !=3D QEMU_PLUGIN_CB= _RW_REGS_PC) > + || (GPOINTER_TO_INT(reg) & 1)) { Maybe this is better as: g_assert(GPOINTER_TO_INT(reg) & 1 =3D=3D 0); if (buf->len =3D=3D 0 || (qemu_plugin_get_cb_flags() !=3D QEMU_PLUGIN= _CB_RW_REGS &&... again the plugin is trying to do something it shouldn't. > return false; > } >=20=20 > - return (gdb_write_register(current_cpu, buf->data, GPOINTER_TO_INT(r= eg) - 1) > 0); > + return (gdb_write_register(current_cpu, buf->data, GPOINTER_TO_INT(r= eg) >> 1) > 0); > } >=20=20 > void qemu_plugin_set_pc(uint64_t vaddr) --=20 Alex Benn=C3=A9e Virtualisation Tech Lead @ Linaro