From: "Steven Rostedt (VMware)" <[email protected]> Andy had some concerns about using regs_get_kernel_stack_nth() in a new function regs_get_kernel_argument() as if there's any error in the stack code, it could cause a bad memory access. To be on the safe side, call probe_kernel_read() on the stack address to be extra careful in accessing the memory. A helper function, regs_get_kernel_stack_nth_addr(), was added to just return the stack address (or NULL if not on the stack), that will be used to find the address (and could be used by other functions) and read the address with kernel_probe_read().
Link: http://lkml.kernel.org/r/calcetrxn9zktb9i1lp3qofcpqzhf34bdkuz5d3n0ucmrr+v...@mail.gmail.com Requested-by: Andy Lutomirski <[email protected]> Signed-off-by: Steven Rostedt (VMware) <[email protected]> --- Changes since v1: - Make regs_get_kernel_stack_nth() not fault, and not have a separate function. Only tracing uses it anyway. arch/x86/include/asm/ptrace.h | 43 ++++++++++++++++++++++++++++++++++++------- 1 file changed, 36 insertions(+), 7 deletions(-) diff --git a/arch/x86/include/asm/ptrace.h b/arch/x86/include/asm/ptrace.h index c2304b25e2fd..055f632ce711 100644 --- a/arch/x86/include/asm/ptrace.h +++ b/arch/x86/include/asm/ptrace.h @@ -237,23 +237,52 @@ static inline int regs_within_kernel_stack(struct pt_regs *regs, } /** + * regs_get_kernel_stack_nth_addr() - get the address of the Nth entry on stack + * @regs: pt_regs which contains kernel stack pointer. + * @n: stack entry number. + * + * regs_get_kernel_stack_nth() returns the address of the @n th entry of the + * kernel stack which is specified by @regs. If the @n th entry is NOT in + * the kernel stack, this returns NULL. + */ +static inline unsigned long *regs_get_kernel_stack_nth_addr(struct pt_regs *regs, + unsigned int n) +{ + unsigned long *addr = (unsigned long *)kernel_stack_pointer(regs); + + addr += n; + if (regs_within_kernel_stack(regs, (unsigned long)addr)) + return addr; + else + return NULL; +} + +/* To avoid include hell, we can't include uaccess.h */ +extern long probe_kernel_read(void *dst, const void *src, size_t size); + +/** * regs_get_kernel_stack_nth() - get Nth entry of the stack * @regs: pt_regs which contains kernel stack pointer. * @n: stack entry number. * * regs_get_kernel_stack_nth() returns @n th entry of the kernel stack which - * is specified by @regs. If the @n th entry is NOT in the kernel stack, + * is specified by @regs. If the @n th entry is NOT in the kernel stack * this returns 0. */ static inline unsigned long regs_get_kernel_stack_nth(struct pt_regs *regs, unsigned int n) { - unsigned long *addr = (unsigned long *)kernel_stack_pointer(regs); - addr += n; - if (regs_within_kernel_stack(regs, (unsigned long)addr)) - return *addr; - else - return 0; + unsigned long *addr; + unsigned long val; + long ret; + + addr = regs_get_kernel_stack_nth_addr(regs, n); + if (addr) { + ret = probe_kernel_read(&val, addr, sizeof(val)); + if (!ret) + return val; + } + return 0; } /** -- 2.13.6
