From: Steven Rostedt (VMware) rostedt@goodmis.org
[ Upstream commit c2712b858187f5bcd7b042fe4daa3ba3a12635c0 ]
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().
Requested-by: Andy Lutomirski luto@amacapital.net Signed-off-by: Steven Rostedt (VMware) rostedt@goodmis.org Reviewed-by: Joel Fernandes (Google) joel@joelfernandes.org Cc: Andy Lutomirski luto@amacapital.net Cc: Borislav Petkov bp@alien8.de Cc: Josh Poimboeuf jpoimboe@redhat.com Cc: Linus Torvalds torvalds@linux-foundation.org Cc: Masami Hiramatsu mhiramat@kernel.org Cc: Peter Zijlstra peterz@infradead.org Cc: Thomas Gleixner tglx@linutronix.de Link: http://lkml.kernel.org/r/20181017165951.09119177@gandalf.local.home Signed-off-by: Ingo Molnar mingo@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- arch/x86/include/asm/ptrace.h | 42 +++++++++++++++++++++++++++++------ 1 file changed, 35 insertions(+), 7 deletions(-)
diff --git a/arch/x86/include/asm/ptrace.h b/arch/x86/include/asm/ptrace.h index 14131dd06b290..8603d127f73c7 100644 --- a/arch/x86/include/asm/ptrace.h +++ b/arch/x86/include/asm/ptrace.h @@ -231,24 +231,52 @@ static inline int regs_within_kernel_stack(struct pt_regs *regs, (kernel_stack_pointer(regs) & ~(THREAD_SIZE - 1))); }
+/** + * 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; }
#define arch_has_single_step() (1)