diff options
author | Linus Torvalds <torvalds@linux-foundation.org> | 2020-11-01 11:21:26 -0800 |
---|---|---|
committer | Linus Torvalds <torvalds@linux-foundation.org> | 2020-11-01 11:21:26 -0800 |
commit | 7b56fbd83e261484da43f04090bce07570bd117f (patch) | |
tree | d8b5e4182098d607c8a15119c55d33d50bc1bc4b | |
parent | 4312e0e8d3eab027d9506db091eb10e6a9ff25d3 (diff) | |
parent | cb05143bdf428f280a5d519c82abf196d7871c11 (diff) | |
download | lwn-7b56fbd83e261484da43f04090bce07570bd117f.tar.gz lwn-7b56fbd83e261484da43f04090bce07570bd117f.zip |
Merge tag 'x86-urgent-2020-11-01' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull x86 fixes from Thomas Gleixner:
"Three fixes all related to #DB:
- Handle the BTF bit correctly so it doesn't get lost due to a kernel
#DB
- Only clear and set the virtual DR6 value used by ptrace on user
space triggered #DB. A kernel #DB must leave it alone to ensure
data consistency for ptrace.
- Make the bitmasking of the virtual DR6 storage correct so it does
not lose DR_STEP"
* tag 'x86-urgent-2020-11-01' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
x86/debug: Fix DR_STEP vs ptrace_get_debugreg(6)
x86/debug: Only clear/set ->virtual_dr6 for userspace #DB
x86/debug: Fix BTF handling
-rw-r--r-- | arch/x86/kernel/traps.c | 43 |
1 files changed, 30 insertions, 13 deletions
diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c index 3c70fb34028b..e19df6cde35d 100644 --- a/arch/x86/kernel/traps.c +++ b/arch/x86/kernel/traps.c @@ -793,19 +793,6 @@ static __always_inline unsigned long debug_read_clear_dr6(void) set_debugreg(DR6_RESERVED, 6); dr6 ^= DR6_RESERVED; /* Flip to positive polarity */ - /* - * Clear the virtual DR6 value, ptrace routines will set bits here for - * things we want signals for. - */ - current->thread.virtual_dr6 = 0; - - /* - * The SDM says "The processor clears the BTF flag when it - * generates a debug exception." Clear TIF_BLOCKSTEP to keep - * TIF_BLOCKSTEP in sync with the hardware BTF flag. - */ - clear_thread_flag(TIF_BLOCKSTEP); - return dr6; } @@ -873,6 +860,20 @@ static __always_inline void exc_debug_kernel(struct pt_regs *regs, */ WARN_ON_ONCE(user_mode(regs)); + if (test_thread_flag(TIF_BLOCKSTEP)) { + /* + * The SDM says "The processor clears the BTF flag when it + * generates a debug exception." but PTRACE_BLOCKSTEP requested + * it for userspace, but we just took a kernel #DB, so re-set + * BTF. + */ + unsigned long debugctl; + + rdmsrl(MSR_IA32_DEBUGCTLMSR, debugctl); + debugctl |= DEBUGCTLMSR_BTF; + wrmsrl(MSR_IA32_DEBUGCTLMSR, debugctl); + } + /* * Catch SYSENTER with TF set and clear DR_STEP. If this hit a * watchpoint at the same time then that will still be handled. @@ -936,6 +937,22 @@ static __always_inline void exc_debug_user(struct pt_regs *regs, instrumentation_begin(); /* + * Start the virtual/ptrace DR6 value with just the DR_STEP mask + * of the real DR6. ptrace_triggered() will set the DR_TRAPn bits. + * + * Userspace expects DR_STEP to be visible in ptrace_get_debugreg(6) + * even if it is not the result of PTRACE_SINGLESTEP. + */ + current->thread.virtual_dr6 = (dr6 & DR_STEP); + + /* + * The SDM says "The processor clears the BTF flag when it + * generates a debug exception." Clear TIF_BLOCKSTEP to keep + * TIF_BLOCKSTEP in sync with the hardware BTF flag. + */ + clear_thread_flag(TIF_BLOCKSTEP); + + /* * If dr6 has no reason to give us about the origin of this trap, * then it's very likely the result of an icebp/int01 trap. * User wants a sigtrap for that. |