* [PATCH] x86/dumpstack: don't dump kernel memory based on usermode RIP
@ 2018-08-28 15:18 Jann Horn
2018-08-28 15:42 ` Kees Cook
0 siblings, 1 reply; 2+ messages in thread
From: Jann Horn @ 2018-08-28 15:18 UTC (permalink / raw)
To: Thomas Gleixner, Ingo Molnar, H. Peter Anvin, x86, jannh
Cc: Borislav Petkov, Andy Lutomirski, linux-kernel, Kees Cook, security
show_opcodes() is used both for dumping kernel instructions and for dumping
user instructions. If userspace causes #PF by jumping to a kernel address,
show_opcodes() can be reached with regs->ip controlled by the user,
pointing to kernel code. Make sure that userspace can't trick us into
dumping kernel memory into dmesg.
Cc: stable@vger.kernel.org
Fixes: 7cccf0725cf7 ("x86/dumpstack: Add a show_ip() function")
Signed-off-by: Jann Horn <jannh@google.com>
---
arch/x86/include/asm/stacktrace.h | 2 +-
arch/x86/kernel/dumpstack.c | 13 ++++++++++---
arch/x86/mm/fault.c | 2 +-
3 files changed, 12 insertions(+), 5 deletions(-)
diff --git a/arch/x86/include/asm/stacktrace.h b/arch/x86/include/asm/stacktrace.h
index b6dc698f992a..f335aad404a4 100644
--- a/arch/x86/include/asm/stacktrace.h
+++ b/arch/x86/include/asm/stacktrace.h
@@ -111,6 +111,6 @@ static inline unsigned long caller_frame_pointer(void)
return (unsigned long)frame;
}
-void show_opcodes(u8 *rip, const char *loglvl);
+void show_opcodes(struct pt_regs *regs, const char *loglvl);
void show_ip(struct pt_regs *regs, const char *loglvl);
#endif /* _ASM_X86_STACKTRACE_H */
diff --git a/arch/x86/kernel/dumpstack.c b/arch/x86/kernel/dumpstack.c
index 9c8652974f8e..5d2700c98b29 100644
--- a/arch/x86/kernel/dumpstack.c
+++ b/arch/x86/kernel/dumpstack.c
@@ -89,14 +89,21 @@ static void printk_stack_address(unsigned long address, int reliable,
* Thus, the 2/3rds prologue and 64 byte OPCODE_BUFSIZE is just a random
* guesstimate in attempt to achieve all of the above.
*/
-void show_opcodes(u8 *rip, const char *loglvl)
+void show_opcodes(struct pt_regs *regs, const char *loglvl)
{
#define PROLOGUE_SIZE 42
#define EPILOGUE_SIZE 21
#define OPCODE_BUFSIZE (PROLOGUE_SIZE + 1 + EPILOGUE_SIZE)
u8 opcodes[OPCODE_BUFSIZE];
+ u8 *prologue = (u8 *)regs->ip - PROLOGUE_SIZE;
+ /*
+ * Make sure userspace isn't trying to trick us into dumping kernel
+ * memory by pointing the userspace instruction pointer at it.
+ */
+ bool bad_ip = user_mode(regs) &&
+ __range_not_ok(prologue, OPCODE_BUFSIZE, TASK_SIZE_MAX);
- if (probe_kernel_read(opcodes, rip - PROLOGUE_SIZE, OPCODE_BUFSIZE)) {
+ if (bad_ip || probe_kernel_read(opcodes, prologue, OPCODE_BUFSIZE)) {
printk("%sCode: Bad RIP value.\n", loglvl);
} else {
printk("%sCode: %" __stringify(PROLOGUE_SIZE) "ph <%02x> %"
@@ -112,7 +119,7 @@ void show_ip(struct pt_regs *regs, const char *loglvl)
#else
printk("%sRIP: %04x:%pS\n", loglvl, (int)regs->cs, (void *)regs->ip);
#endif
- show_opcodes((u8 *)regs->ip, loglvl);
+ show_opcodes(regs, loglvl);
}
void show_iret_regs(struct pt_regs *regs)
diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index b9123c497e0a..47bebfe6efa7 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -837,7 +837,7 @@ show_signal_msg(struct pt_regs *regs, unsigned long error_code,
printk(KERN_CONT "\n");
- show_opcodes((u8 *)regs->ip, loglvl);
+ show_opcodes(regs, loglvl);
}
static void
--
2.19.0.rc0.228.g281dcd1b4d0-goog
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH] x86/dumpstack: don't dump kernel memory based on usermode RIP
2018-08-28 15:18 [PATCH] x86/dumpstack: don't dump kernel memory based on usermode RIP Jann Horn
@ 2018-08-28 15:42 ` Kees Cook
0 siblings, 0 replies; 2+ messages in thread
From: Kees Cook @ 2018-08-28 15:42 UTC (permalink / raw)
To: Jann Horn
Cc: Thomas Gleixner, Ingo Molnar, H. Peter Anvin, X86 ML,
Borislav Petkov, Andy Lutomirski, LKML, Security Officers
On Tue, Aug 28, 2018 at 8:18 AM, Jann Horn <jannh@google.com> wrote:
> show_opcodes() is used both for dumping kernel instructions and for dumping
> user instructions. If userspace causes #PF by jumping to a kernel address,
> show_opcodes() can be reached with regs->ip controlled by the user,
> pointing to kernel code. Make sure that userspace can't trick us into
> dumping kernel memory into dmesg.
>
> Cc: stable@vger.kernel.org
> Fixes: 7cccf0725cf7 ("x86/dumpstack: Add a show_ip() function")
> Signed-off-by: Jann Horn <jannh@google.com>
Thanks for finding this!
Reviewed-by: Kees Cook <keescook@chromium.org>
-Kees
> ---
> arch/x86/include/asm/stacktrace.h | 2 +-
> arch/x86/kernel/dumpstack.c | 13 ++++++++++---
> arch/x86/mm/fault.c | 2 +-
> 3 files changed, 12 insertions(+), 5 deletions(-)
>
> diff --git a/arch/x86/include/asm/stacktrace.h b/arch/x86/include/asm/stacktrace.h
> index b6dc698f992a..f335aad404a4 100644
> --- a/arch/x86/include/asm/stacktrace.h
> +++ b/arch/x86/include/asm/stacktrace.h
> @@ -111,6 +111,6 @@ static inline unsigned long caller_frame_pointer(void)
> return (unsigned long)frame;
> }
>
> -void show_opcodes(u8 *rip, const char *loglvl);
> +void show_opcodes(struct pt_regs *regs, const char *loglvl);
> void show_ip(struct pt_regs *regs, const char *loglvl);
> #endif /* _ASM_X86_STACKTRACE_H */
> diff --git a/arch/x86/kernel/dumpstack.c b/arch/x86/kernel/dumpstack.c
> index 9c8652974f8e..5d2700c98b29 100644
> --- a/arch/x86/kernel/dumpstack.c
> +++ b/arch/x86/kernel/dumpstack.c
> @@ -89,14 +89,21 @@ static void printk_stack_address(unsigned long address, int reliable,
> * Thus, the 2/3rds prologue and 64 byte OPCODE_BUFSIZE is just a random
> * guesstimate in attempt to achieve all of the above.
> */
> -void show_opcodes(u8 *rip, const char *loglvl)
> +void show_opcodes(struct pt_regs *regs, const char *loglvl)
> {
> #define PROLOGUE_SIZE 42
> #define EPILOGUE_SIZE 21
> #define OPCODE_BUFSIZE (PROLOGUE_SIZE + 1 + EPILOGUE_SIZE)
> u8 opcodes[OPCODE_BUFSIZE];
> + u8 *prologue = (u8 *)regs->ip - PROLOGUE_SIZE;
> + /*
> + * Make sure userspace isn't trying to trick us into dumping kernel
> + * memory by pointing the userspace instruction pointer at it.
> + */
> + bool bad_ip = user_mode(regs) &&
> + __range_not_ok(prologue, OPCODE_BUFSIZE, TASK_SIZE_MAX);
>
> - if (probe_kernel_read(opcodes, rip - PROLOGUE_SIZE, OPCODE_BUFSIZE)) {
> + if (bad_ip || probe_kernel_read(opcodes, prologue, OPCODE_BUFSIZE)) {
> printk("%sCode: Bad RIP value.\n", loglvl);
> } else {
> printk("%sCode: %" __stringify(PROLOGUE_SIZE) "ph <%02x> %"
> @@ -112,7 +119,7 @@ void show_ip(struct pt_regs *regs, const char *loglvl)
> #else
> printk("%sRIP: %04x:%pS\n", loglvl, (int)regs->cs, (void *)regs->ip);
> #endif
> - show_opcodes((u8 *)regs->ip, loglvl);
> + show_opcodes(regs, loglvl);
> }
>
> void show_iret_regs(struct pt_regs *regs)
> diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
> index b9123c497e0a..47bebfe6efa7 100644
> --- a/arch/x86/mm/fault.c
> +++ b/arch/x86/mm/fault.c
> @@ -837,7 +837,7 @@ show_signal_msg(struct pt_regs *regs, unsigned long error_code,
>
> printk(KERN_CONT "\n");
>
> - show_opcodes((u8 *)regs->ip, loglvl);
> + show_opcodes(regs, loglvl);
> }
>
> static void
> --
> 2.19.0.rc0.228.g281dcd1b4d0-goog
>
--
Kees Cook
Pixel Security
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