| Message ID | 20140730071245.GA8954@mew.web-pass.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Wed, Jul 30, 2014 at 12:12:45AM -0700, Omar Sandoval wrote: > The kgdb breakpoint hooks (kgdb_brk_fn and kgdb_compiled_brk_fn) should only be > entered when a kgdb break instruction is executed from the kernel. Otherwise, > if kgdb is enabled, a userspace program can cause the kernel to drop into the > debugger by executing either KGDB_BREAKINST or KGDB_COMPILED_BREAK on ARM, or > brk #KGDB_{DYN,COMPILED}_DGB_BRK_IMM on ARM64. > > Signed-off-by: Omar Sandoval <osandov@osandov.com> > --- > The following program reproduces the fixed problem on ARM: > .globl _start > _start: > udf #65006 @ KGDB_BREAKINST > > And on ARM64: > .globl _start > _start: > brk #0x400 @ KGDB_DYN_DGB_BRK_IMM > > arch/arm/kernel/kgdb.c | 4 ++++ > arch/arm64/include/asm/debug-monitors.h | 4 +++- > arch/arm64/kernel/debug-monitors.c | 3 ++- > arch/arm64/kernel/kgdb.c | 4 ++++ > 4 files changed, 13 insertions(+), 2 deletions(-) > > diff --git a/arch/arm/kernel/kgdb.c b/arch/arm/kernel/kgdb.c > index 778c2f7..a74b53c 100644 > --- a/arch/arm/kernel/kgdb.c > +++ b/arch/arm/kernel/kgdb.c > @@ -160,12 +160,16 @@ static int kgdb_compiled_brk_fn(struct pt_regs *regs, unsigned int instr) > static struct undef_hook kgdb_brkpt_hook = { > .instr_mask = 0xffffffff, > .instr_val = KGDB_BREAKINST, > + .cpsr_mask = MODE_MASK, > + .cpsr_val = SVC_MODE, > .fn = kgdb_brk_fn > }; > > static struct undef_hook kgdb_compiled_brkpt_hook = { > .instr_mask = 0xffffffff, > .instr_val = KGDB_COMPILED_BREAK, > + .cpsr_mask = MODE_MASK, > + .cpsr_val = SVC_MODE, > .fn = kgdb_compiled_brk_fn > }; > > diff --git a/arch/arm64/include/asm/debug-monitors.h b/arch/arm64/include/asm/debug-monitors.h > index 6e9b5b3..e1d27ce 100644 > --- a/arch/arm64/include/asm/debug-monitors.h > +++ b/arch/arm64/include/asm/debug-monitors.h > @@ -105,8 +105,10 @@ void unregister_step_hook(struct step_hook *hook); > > struct break_hook { > struct list_head node; > - u32 esr_val; > u32 esr_mask; > + u32 esr_val; > + u64 pstate_mask; > + u64 pstate_val; > int (*fn)(struct pt_regs *regs, unsigned int esr); > }; > > diff --git a/arch/arm64/kernel/debug-monitors.c b/arch/arm64/kernel/debug-monitors.c > index a7fb874..594fac4 100644 > --- a/arch/arm64/kernel/debug-monitors.c > +++ b/arch/arm64/kernel/debug-monitors.c > @@ -303,7 +303,8 @@ static int call_break_hook(struct pt_regs *regs, unsigned int esr) > > read_lock(&break_hook_lock); > list_for_each_entry(hook, &break_hook, node) > - if ((esr & hook->esr_mask) == hook->esr_val) > + if ((esr & hook->esr_mask) == hook->esr_val && > + (regs->pstate & hook->pstate_mask) == hook->pstate_val) > fn = hook->fn; > read_unlock(&break_hook_lock); > > diff --git a/arch/arm64/kernel/kgdb.c b/arch/arm64/kernel/kgdb.c > index 75c9cf1..80eb035 100644 > --- a/arch/arm64/kernel/kgdb.c > +++ b/arch/arm64/kernel/kgdb.c > @@ -236,12 +236,16 @@ static int kgdb_step_brk_fn(struct pt_regs *regs, unsigned int esr) > static struct break_hook kgdb_brkpt_hook = { > .esr_mask = 0xffffffff, > .esr_val = DBG_ESR_VAL_BRK(KGDB_DYN_DGB_BRK_IMM), > + .pstate_mask = PSR_MODE_MASK, > + .pstate_val = PSR_MODE_EL1h, > .fn = kgdb_brk_fn > }; > > static struct break_hook kgdb_compiled_brkpt_hook = { > .esr_mask = 0xffffffff, > .esr_val = DBG_ESR_VAL_BRK(KDBG_COMPILED_DBG_BRK_IMM), > + .pstate_mask = PSR_MODE_MASK, > + .pstate_val = PSR_MODE_EL1h, > .fn = kgdb_compiled_brk_fn > }; > > -- > 2.0.3 >
diff --git a/arch/arm/kernel/kgdb.c b/arch/arm/kernel/kgdb.c index 778c2f7..a74b53c 100644 --- a/arch/arm/kernel/kgdb.c +++ b/arch/arm/kernel/kgdb.c @@ -160,12 +160,16 @@ static int kgdb_compiled_brk_fn(struct pt_regs *regs, unsigned int instr) static struct undef_hook kgdb_brkpt_hook = { .instr_mask = 0xffffffff, .instr_val = KGDB_BREAKINST, + .cpsr_mask = MODE_MASK, + .cpsr_val = SVC_MODE, .fn = kgdb_brk_fn }; static struct undef_hook kgdb_compiled_brkpt_hook = { .instr_mask = 0xffffffff, .instr_val = KGDB_COMPILED_BREAK, + .cpsr_mask = MODE_MASK, + .cpsr_val = SVC_MODE, .fn = kgdb_compiled_brk_fn }; diff --git a/arch/arm64/include/asm/debug-monitors.h b/arch/arm64/include/asm/debug-monitors.h index 6e9b5b3..e1d27ce 100644 --- a/arch/arm64/include/asm/debug-monitors.h +++ b/arch/arm64/include/asm/debug-monitors.h @@ -105,8 +105,10 @@ void unregister_step_hook(struct step_hook *hook); struct break_hook { struct list_head node; - u32 esr_val; u32 esr_mask; + u32 esr_val; + u64 pstate_mask; + u64 pstate_val; int (*fn)(struct pt_regs *regs, unsigned int esr); }; diff --git a/arch/arm64/kernel/debug-monitors.c b/arch/arm64/kernel/debug-monitors.c index a7fb874..594fac4 100644 --- a/arch/arm64/kernel/debug-monitors.c +++ b/arch/arm64/kernel/debug-monitors.c @@ -303,7 +303,8 @@ static int call_break_hook(struct pt_regs *regs, unsigned int esr) read_lock(&break_hook_lock); list_for_each_entry(hook, &break_hook, node) - if ((esr & hook->esr_mask) == hook->esr_val) + if ((esr & hook->esr_mask) == hook->esr_val && + (regs->pstate & hook->pstate_mask) == hook->pstate_val) fn = hook->fn; read_unlock(&break_hook_lock); diff --git a/arch/arm64/kernel/kgdb.c b/arch/arm64/kernel/kgdb.c index 75c9cf1..80eb035 100644 --- a/arch/arm64/kernel/kgdb.c +++ b/arch/arm64/kernel/kgdb.c @@ -236,12 +236,16 @@ static int kgdb_step_brk_fn(struct pt_regs *regs, unsigned int esr) static struct break_hook kgdb_brkpt_hook = { .esr_mask = 0xffffffff, .esr_val = DBG_ESR_VAL_BRK(KGDB_DYN_DGB_BRK_IMM), + .pstate_mask = PSR_MODE_MASK, + .pstate_val = PSR_MODE_EL1h, .fn = kgdb_brk_fn }; static struct break_hook kgdb_compiled_brkpt_hook = { .esr_mask = 0xffffffff, .esr_val = DBG_ESR_VAL_BRK(KDBG_COMPILED_DBG_BRK_IMM), + .pstate_mask = PSR_MODE_MASK, + .pstate_val = PSR_MODE_EL1h, .fn = kgdb_compiled_brk_fn };
The kgdb breakpoint hooks (kgdb_brk_fn and kgdb_compiled_brk_fn) should only be entered when a kgdb break instruction is executed from the kernel. Otherwise, if kgdb is enabled, a userspace program can cause the kernel to drop into the debugger by executing either KGDB_BREAKINST or KGDB_COMPILED_BREAK on ARM, or brk #KGDB_{DYN,COMPILED}_DGB_BRK_IMM on ARM64. Signed-off-by: Omar Sandoval <osandov@osandov.com> --- The following program reproduces the fixed problem on ARM: .globl _start _start: udf #65006 @ KGDB_BREAKINST And on ARM64: .globl _start _start: brk #0x400 @ KGDB_DYN_DGB_BRK_IMM arch/arm/kernel/kgdb.c | 4 ++++ arch/arm64/include/asm/debug-monitors.h | 4 +++- arch/arm64/kernel/debug-monitors.c | 3 ++- arch/arm64/kernel/kgdb.c | 4 ++++ 4 files changed, 13 insertions(+), 2 deletions(-)