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Miller" , Mathieu Desnoyers , linux-trace-kernel@vger.kernel.org Cc: Jinchao Wang Subject: [PATCH v6 14/23] mm/ksw: resolve stack watch addr and len Date: Tue, 30 Sep 2025 10:43:35 +0800 Message-ID: <20250930024402.1043776-15-wangjinchao600@gmail.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20250930024402.1043776-1-wangjinchao600@gmail.com> References: <20250930024402.1043776-1-wangjinchao600@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Add helpers to find the stack canary or a local variable addr and len for the probed function based on ksw_get_config(). For canary search, limits search to a fixed number of steps to avoid scanning the entire stack. Validates that the computed address and length are within the kernel stack. Signed-off-by: Jinchao Wang --- mm/kstackwatch/stack.c | 77 ++++++++++++++++++++++++++++++++++++++++-- 1 file changed, 74 insertions(+), 3 deletions(-) diff --git a/mm/kstackwatch/stack.c b/mm/kstackwatch/stack.c index e596ef97222d..3c4cb6d5b58a 100644 --- a/mm/kstackwatch/stack.c +++ b/mm/kstackwatch/stack.c @@ -9,6 +9,7 @@ =20 #include "kstackwatch.h" =20 +#define MAX_CANARY_SEARCH_STEPS 128 static struct kprobe entry_probe; static struct fprobe exit_probe; =20 @@ -59,13 +60,83 @@ static bool ksw_stack_check_ctx(bool entry) return false; } =20 +static unsigned long ksw_find_stack_canary_addr(struct pt_regs *regs) +{ + unsigned long *stack_ptr, *stack_end, *stack_base; + unsigned long expected_canary; + unsigned int i; + + stack_ptr =3D (unsigned long *)kernel_stack_pointer(regs); + + stack_base =3D (unsigned long *)(current->stack); + + // TODO: limit it to the current frame + stack_end =3D (unsigned long *)((char *)current->stack + THREAD_SIZE); + + expected_canary =3D current->stack_canary; + + if (stack_ptr < stack_base || stack_ptr >=3D stack_end) { + pr_err("Stack pointer 0x%lx out of bounds [0x%lx, 0x%lx)\n", + (unsigned long)stack_ptr, (unsigned long)stack_base, + (unsigned long)stack_end); + return 0; + } + + for (i =3D 0; i < MAX_CANARY_SEARCH_STEPS; i++) { + if (&stack_ptr[i] >=3D stack_end) + break; + + if (stack_ptr[i] =3D=3D expected_canary) { + pr_debug("canary found i:%d 0x%lx\n", i, + (unsigned long)&stack_ptr[i]); + return (unsigned long)&stack_ptr[i]; + } + } + + pr_debug("canary not found in first %d steps\n", + MAX_CANARY_SEARCH_STEPS); + return 0; +} + +static int ksw_stack_validate_addr(unsigned long addr, size_t size) +{ + unsigned long stack_start, stack_end; + + if (!addr || !size) + return -EINVAL; + + stack_start =3D (unsigned long)current->stack; + stack_end =3D stack_start + THREAD_SIZE; + + if (addr < stack_start || (addr + size) > stack_end) + return -ERANGE; + + return 0; +} + static int ksw_stack_prepare_watch(struct pt_regs *regs, const struct ksw_config *config, ulong *watch_addr, u16 *watch_len) { - /* implement logic will be added in following patches */ - *watch_addr =3D 0; - *watch_len =3D 0; + ulong addr; + u16 len; + + // default is to watch the canary + if (!ksw_get_config()->watch_len) { + addr =3D ksw_find_stack_canary_addr(regs); + len =3D sizeof(ulong); + } else { + addr =3D kernel_stack_pointer(regs) + ksw_get_config()->sp_offset; + len =3D ksw_get_config()->watch_len; + } + + if (ksw_stack_validate_addr(addr, len)) { + pr_err("invalid stack addr:0x%lx len :%u\n", addr, len); + return -EINVAL; + } + + *watch_addr =3D addr; + *watch_len =3D len; return 0; } =20 --=20 2.43.0