Messages in this thread Patch in this message | | | Date | Fri, 31 Aug 2018 10:04:41 +0200 | From | Borislav Petkov <> | Subject | Re: [PATCH] x86/dumpstack: fix address space casting in show_opcodes() |
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On Thu, Aug 30, 2018 at 09:47:36PM +0200, Jann Horn wrote: > I sloppily passed a kernel-typed pointer to __range_not_ok(), and sparse > doesn't like that. > Make `prologue` a __user pointer (to protect against accidental > dereferences) and force-cast it to a kernel pointer when calling > probe_kernel_read(), which will then immediately force-cast it back to a > user pointer.
Yeah, that's some crazy casting.
Can we define a local __user pointer only for the check instead? It is less casting and looks simpler and actually even easier to understand what we're doing...
--- diff --git a/arch/x86/kernel/dumpstack.c b/arch/x86/kernel/dumpstack.c index 605c60b1624f..9c5a15491108 100644 --- a/arch/x86/kernel/dumpstack.c +++ b/arch/x86/kernel/dumpstack.c @@ -97,14 +97,17 @@ void show_opcodes(struct pt_regs *regs, const char *loglvl) #define OPCODE_BUFSIZE (PROLOGUE_SIZE + 1 + EPILOGUE_SIZE) u8 opcodes[OPCODE_BUFSIZE]; u8 *prologue = (u8 *)(regs->ip - PROLOGUE_SIZE); - bool bad_ip; + bool bad_ip = false; /* * Make sure userspace isn't trying to trick us into dumping kernel * memory by pointing the userspace instruction pointer at it. */ - bad_ip = user_mode(regs) && - __range_not_ok(prologue, OPCODE_BUFSIZE, TASK_SIZE_MAX); + if (user_mode(regs)) { + u8 __user *up = (u8 __user *)prologue; + + bad_ip = __range_not_ok(up, OPCODE_BUFSIZE, TASK_SIZE_MAX); + } if (bad_ip || probe_kernel_read(opcodes, prologue, OPCODE_BUFSIZE)) { printk("%sCode: Bad RIP value.\n", loglvl); -- Regards/Gruss, Boris.
SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg) --
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