* [patch v2 0/2] x86/dumpstack: Prevent access to foreign tasks user space
@ 2020-11-17 20:23 Thomas Gleixner
2020-11-17 20:23 ` [patch v2 1/2] x86/dumpstack: Dont try to access user space code of other tasks Thomas Gleixner
2020-11-17 20:23 ` [patch v2 2/2] x86/uaccess: Document copy_from_user_nmi() Thomas Gleixner
0 siblings, 2 replies; 5+ messages in thread
From: Thomas Gleixner @ 2020-11-17 20:23 UTC (permalink / raw)
To: LKML; +Cc: Oleg Nesterov, Mark Mossberg, Ingo Molnar, X86 ML, Jann Horn, kyin
This is the second version of the patch to prevent access to a foreign
tasks user space in copy_code(). It addresses the review comments from
Boris and adds a new patch which provides documentation for
copy_from_user_nmi() to avoid further confusion about it's usage.
V1 can be found here:
https://lore.kernel.org/r/87blfxx8ps.fsf@nanos.tec.linutronix.de
Thanks,
tglx
^ permalink raw reply [flat|nested] 5+ messages in thread
* [patch v2 1/2] x86/dumpstack: Dont try to access user space code of other tasks
2020-11-17 20:23 [patch v2 0/2] x86/dumpstack: Prevent access to foreign tasks user space Thomas Gleixner
@ 2020-11-17 20:23 ` Thomas Gleixner
2020-11-18 12:20 ` [tip: x86/urgent] x86/dumpstack: Do not " tip-bot2 for Thomas Gleixner
2020-11-17 20:23 ` [patch v2 2/2] x86/uaccess: Document copy_from_user_nmi() Thomas Gleixner
1 sibling, 1 reply; 5+ messages in thread
From: Thomas Gleixner @ 2020-11-17 20:23 UTC (permalink / raw)
To: LKML
Cc: Oleg Nesterov, Mark Mossberg, Ingo Molnar, X86 ML, Jann Horn,
kyin, Borislav Petkov
sysrq-t ends up invoking show_opcodes() for each task which tries to access
the user space code of other processes which is obviously bogus.
It either manages to dump where the foreign tasks regs->ip points to in a
valid mapping of the current task or triggers a pagefault and prints "Code:
Bad RIP value.". Both is just wrong.
Add a safeguard in copy_code() and check whether the @regs pointer matches
currents pt_regs. If not, do not even try to access it.
While at it, add commentary why using copy_from_user_nmi() is safe in
copy_code() even if the function name suggests otherwise.
Reported-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Borislav Petkov <bp@suse.de>
Tested-by: Borislav Petkov <bp@suse.de>
Acked-by: Oleg Nesterov <oleg@redhat.com>
Link: https://lore.kernel.org/r/87blfxx8ps.fsf@nanos.tec.linutronix.de
---
V2: Fixed changelog, comment and Reported-by attribution (Boris)
---
arch/x86/kernel/dumpstack.c | 23 +++++++++++++++++++----
1 file changed, 19 insertions(+), 4 deletions(-)
--- a/arch/x86/kernel/dumpstack.c
+++ b/arch/x86/kernel/dumpstack.c
@@ -78,6 +78,9 @@ static int copy_code(struct pt_regs *reg
if (!user_mode(regs))
return copy_from_kernel_nofault(buf, (u8 *)src, nbytes);
+ /* The user space code from other tasks cannot be accessed. */
+ if (regs != task_pt_regs(current))
+ return -EPERM;
/*
* Make sure userspace isn't trying to trick us into dumping kernel
* memory by pointing the userspace instruction pointer at it.
@@ -85,6 +88,12 @@ static int copy_code(struct pt_regs *reg
if (__chk_range_not_ok(src, nbytes, TASK_SIZE_MAX))
return -EINVAL;
+ /*
+ * Even if named copy_from_user_nmi() this can be invoked from
+ * other contexts and will not try to resolve a pagefault, which is
+ * the correct thing to do here as this code can be called from any
+ * context.
+ */
return copy_from_user_nmi(buf, (void __user *)src, nbytes);
}
@@ -115,13 +124,19 @@ void show_opcodes(struct pt_regs *regs,
u8 opcodes[OPCODE_BUFSIZE];
unsigned long prologue = regs->ip - PROLOGUE_SIZE;
- if (copy_code(regs, opcodes, prologue, sizeof(opcodes))) {
- printk("%sCode: Unable to access opcode bytes at RIP 0x%lx.\n",
- loglvl, prologue);
- } else {
+ switch (copy_code(regs, opcodes, prologue, sizeof(opcodes))) {
+ case 0:
printk("%sCode: %" __stringify(PROLOGUE_SIZE) "ph <%02x> %"
__stringify(EPILOGUE_SIZE) "ph\n", loglvl, opcodes,
opcodes[PROLOGUE_SIZE], opcodes + PROLOGUE_SIZE + 1);
+ break;
+ case -EPERM:
+ /* No access to the user space stack of other tasks. Ignore. */
+ break;
+ default:
+ printk("%sCode: Unable to access opcode bytes at RIP 0x%lx.\n",
+ loglvl, prologue);
+ break;
}
}
^ permalink raw reply [flat|nested] 5+ messages in thread
* [patch v2 2/2] x86/uaccess: Document copy_from_user_nmi()
2020-11-17 20:23 [patch v2 0/2] x86/dumpstack: Prevent access to foreign tasks user space Thomas Gleixner
2020-11-17 20:23 ` [patch v2 1/2] x86/dumpstack: Dont try to access user space code of other tasks Thomas Gleixner
@ 2020-11-17 20:23 ` Thomas Gleixner
2020-11-18 12:31 ` [tip: x86/cleanups] " tip-bot2 for Thomas Gleixner
1 sibling, 1 reply; 5+ messages in thread
From: Thomas Gleixner @ 2020-11-17 20:23 UTC (permalink / raw)
To: LKML
Cc: Oleg Nesterov, Mark Mossberg, Ingo Molnar, X86 ML, Jann Horn,
kyin, Borislav Petkov
Document the functionality of copy_from_user_nmi() to avoid further
confusion. Fix the typo in the existing comment while at it.
Requested-by: Borislav Petkov <bp@alien8.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
V2: New patch
---
arch/x86/lib/usercopy.c | 22 ++++++++++++++++++----
1 file changed, 18 insertions(+), 4 deletions(-)
--- a/arch/x86/lib/usercopy.c
+++ b/arch/x86/lib/usercopy.c
@@ -9,9 +9,23 @@
#include <asm/tlbflush.h>
-/*
- * We rely on the nested NMI work to allow atomic faults from the NMI path; the
- * nested NMI paths are careful to preserve CR2.
+/**
+ * copy_from_user_nmi - NMI safe copy from user
+ * @to: Pointer to the destination buffer
+ * @from: Pointer to a user space address of the current task
+ * @n: Number of bytes to copy
+ *
+ * Returns: The number of not copied bytes. 0 is success, i.e. all bytes copied
+ *
+ * Contrary to other copy_from_user() variants this function can be called
+ * from NMI context. Despite the name it is not restricted to be called
+ * from NMI context. It is safe to be called from any other context as
+ * well. It disables pagefaults across the copy which means a fault will
+ * abort the copy.
+ *
+ * For NMI context invocations this relies on the nested NMI work to allow
+ * atomic faults from the NMI path; the nested NMI paths are careful to
+ * preserve CR2.
*/
unsigned long
copy_from_user_nmi(void *to, const void __user *from, unsigned long n)
@@ -27,7 +41,7 @@ copy_from_user_nmi(void *to, const void
/*
* Even though this function is typically called from NMI/IRQ context
* disable pagefaults so that its behaviour is consistent even when
- * called form other contexts.
+ * called from other contexts.
*/
pagefault_disable();
ret = __copy_from_user_inatomic(to, from, n);
^ permalink raw reply [flat|nested] 5+ messages in thread
* [tip: x86/urgent] x86/dumpstack: Do not try to access user space code of other tasks
2020-11-17 20:23 ` [patch v2 1/2] x86/dumpstack: Dont try to access user space code of other tasks Thomas Gleixner
@ 2020-11-18 12:20 ` tip-bot2 for Thomas Gleixner
0 siblings, 0 replies; 5+ messages in thread
From: tip-bot2 for Thomas Gleixner @ 2020-11-18 12:20 UTC (permalink / raw)
To: linux-tip-commits
Cc: Oleg Nesterov, Thomas Gleixner, Borislav Petkov, x86, linux-kernel
The following commit has been merged into the x86/urgent branch of tip:
Commit-ID: 860aaabac8235cfde10fe556aa82abbbe3117888
Gitweb: https://git.kernel.org/tip/860aaabac8235cfde10fe556aa82abbbe3117888
Author: Thomas Gleixner <tglx@linutronix.de>
AuthorDate: Tue, 17 Nov 2020 21:23:34 +01:00
Committer: Borislav Petkov <bp@suse.de>
CommitterDate: Wed, 18 Nov 2020 12:56:29 +01:00
x86/dumpstack: Do not try to access user space code of other tasks
sysrq-t ends up invoking show_opcodes() for each task which tries to access
the user space code of other processes, which is obviously bogus.
It either manages to dump where the foreign task's regs->ip points to in a
valid mapping of the current task or triggers a pagefault and prints "Code:
Bad RIP value.". Both is just wrong.
Add a safeguard in copy_code() and check whether the @regs pointer matches
currents pt_regs. If not, do not even try to access it.
While at it, add commentary why using copy_from_user_nmi() is safe in
copy_code() even if the function name suggests otherwise.
Reported-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Borislav Petkov <bp@suse.de>
Acked-by: Oleg Nesterov <oleg@redhat.com>
Tested-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20201117202753.667274723@linutronix.de
---
arch/x86/kernel/dumpstack.c | 23 +++++++++++++++++++----
1 file changed, 19 insertions(+), 4 deletions(-)
diff --git a/arch/x86/kernel/dumpstack.c b/arch/x86/kernel/dumpstack.c
index 25c06b6..97aa900 100644
--- a/arch/x86/kernel/dumpstack.c
+++ b/arch/x86/kernel/dumpstack.c
@@ -78,6 +78,9 @@ static int copy_code(struct pt_regs *regs, u8 *buf, unsigned long src,
if (!user_mode(regs))
return copy_from_kernel_nofault(buf, (u8 *)src, nbytes);
+ /* The user space code from other tasks cannot be accessed. */
+ if (regs != task_pt_regs(current))
+ return -EPERM;
/*
* Make sure userspace isn't trying to trick us into dumping kernel
* memory by pointing the userspace instruction pointer at it.
@@ -85,6 +88,12 @@ static int copy_code(struct pt_regs *regs, u8 *buf, unsigned long src,
if (__chk_range_not_ok(src, nbytes, TASK_SIZE_MAX))
return -EINVAL;
+ /*
+ * Even if named copy_from_user_nmi() this can be invoked from
+ * other contexts and will not try to resolve a pagefault, which is
+ * the correct thing to do here as this code can be called from any
+ * context.
+ */
return copy_from_user_nmi(buf, (void __user *)src, nbytes);
}
@@ -115,13 +124,19 @@ void show_opcodes(struct pt_regs *regs, const char *loglvl)
u8 opcodes[OPCODE_BUFSIZE];
unsigned long prologue = regs->ip - PROLOGUE_SIZE;
- if (copy_code(regs, opcodes, prologue, sizeof(opcodes))) {
- printk("%sCode: Unable to access opcode bytes at RIP 0x%lx.\n",
- loglvl, prologue);
- } else {
+ switch (copy_code(regs, opcodes, prologue, sizeof(opcodes))) {
+ case 0:
printk("%sCode: %" __stringify(PROLOGUE_SIZE) "ph <%02x> %"
__stringify(EPILOGUE_SIZE) "ph\n", loglvl, opcodes,
opcodes[PROLOGUE_SIZE], opcodes + PROLOGUE_SIZE + 1);
+ break;
+ case -EPERM:
+ /* No access to the user space stack of other tasks. Ignore. */
+ break;
+ default:
+ printk("%sCode: Unable to access opcode bytes at RIP 0x%lx.\n",
+ loglvl, prologue);
+ break;
}
}
^ permalink raw reply related [flat|nested] 5+ messages in thread
* [tip: x86/cleanups] x86/uaccess: Document copy_from_user_nmi()
2020-11-17 20:23 ` [patch v2 2/2] x86/uaccess: Document copy_from_user_nmi() Thomas Gleixner
@ 2020-11-18 12:31 ` tip-bot2 for Thomas Gleixner
0 siblings, 0 replies; 5+ messages in thread
From: tip-bot2 for Thomas Gleixner @ 2020-11-18 12:31 UTC (permalink / raw)
To: linux-tip-commits; +Cc: Thomas Gleixner, Borislav Petkov, x86, linux-kernel
The following commit has been merged into the x86/cleanups branch of tip:
Commit-ID: 907f8eb8e0eb2b3312b292e67dc4dbc493424747
Gitweb: https://git.kernel.org/tip/907f8eb8e0eb2b3312b292e67dc4dbc493424747
Author: Thomas Gleixner <tglx@linutronix.de>
AuthorDate: Tue, 17 Nov 2020 21:23:35 +01:00
Committer: Borislav Petkov <bp@suse.de>
CommitterDate: Wed, 18 Nov 2020 13:19:01 +01:00
x86/uaccess: Document copy_from_user_nmi()
Document the functionality of copy_from_user_nmi() to avoid further
confusion. Fix the typo in the existing comment while at it.
Requested-by: Borislav Petkov <bp@alien8.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20201117202753.806376613@linutronix.de
---
arch/x86/lib/usercopy.c | 22 ++++++++++++++++++----
1 file changed, 18 insertions(+), 4 deletions(-)
diff --git a/arch/x86/lib/usercopy.c b/arch/x86/lib/usercopy.c
index 3f435d7..c3e8a62 100644
--- a/arch/x86/lib/usercopy.c
+++ b/arch/x86/lib/usercopy.c
@@ -9,9 +9,23 @@
#include <asm/tlbflush.h>
-/*
- * We rely on the nested NMI work to allow atomic faults from the NMI path; the
- * nested NMI paths are careful to preserve CR2.
+/**
+ * copy_from_user_nmi - NMI safe copy from user
+ * @to: Pointer to the destination buffer
+ * @from: Pointer to a user space address of the current task
+ * @n: Number of bytes to copy
+ *
+ * Returns: The number of not copied bytes. 0 is success, i.e. all bytes copied
+ *
+ * Contrary to other copy_from_user() variants this function can be called
+ * from NMI context. Despite the name it is not restricted to be called
+ * from NMI context. It is safe to be called from any other context as
+ * well. It disables pagefaults across the copy which means a fault will
+ * abort the copy.
+ *
+ * For NMI context invocations this relies on the nested NMI work to allow
+ * atomic faults from the NMI path; the nested NMI paths are careful to
+ * preserve CR2.
*/
unsigned long
copy_from_user_nmi(void *to, const void __user *from, unsigned long n)
@@ -27,7 +41,7 @@ copy_from_user_nmi(void *to, const void __user *from, unsigned long n)
/*
* Even though this function is typically called from NMI/IRQ context
* disable pagefaults so that its behaviour is consistent even when
- * called form other contexts.
+ * called from other contexts.
*/
pagefault_disable();
ret = __copy_from_user_inatomic(to, from, n);
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