Message ID | 20210604112450.13344-3-broonie@kernel.org |
---|---|
State | New |
Headers | show |
Series | arm64: Enable BTI for the executable as well as the interpreter | expand |
On Fri, Jun 04, 2021 at 12:24:49PM +0100, Mark Brown wrote: > Currently for dynamically linked ELF executables we only enable BTI for > the interpreter, expecting the interpreter to do this for the main > executable. This is a bit inconsistent since we do map main executable and > is causing issues with systemd's MemoryDenyWriteExecute feature which is > implemented using a seccomp filter which prevents setting PROT_EXEC on > already mapped memory and lacks the context to be able to detect that > memory is already mapped with PROT_EXEC. > > Resolve this by checking the BTI property for the main executable and > enabling BTI if it is present when doing the initial mapping. This does > mean that we may get more code with BTI enabled if running on a system > without BTI support in the dynamic linker, this is expected to be a safe > configuration and testing seems to confirm that. It also reduces the > flexibility userspace has to disable BTI but it is expected that for cases > where there are problems which require BTI to be disabled it is more likely > that it will need to be disabled on a system level. > > Signed-off-by: Mark Brown <broonie@kernel.org> > Reviewed-by: Dave Martin <Dave.Martin@arm.com> > --- > arch/arm64/include/asm/elf.h | 14 ++++++++++---- > arch/arm64/kernel/process.c | 18 ++++++------------ > 2 files changed, 16 insertions(+), 16 deletions(-) > > diff --git a/arch/arm64/include/asm/elf.h b/arch/arm64/include/asm/elf.h > index a488a1329b16..9f86dbce2680 100644 > --- a/arch/arm64/include/asm/elf.h > +++ b/arch/arm64/include/asm/elf.h > @@ -253,7 +253,8 @@ struct arch_elf_state { > int flags; > }; > > -#define ARM64_ELF_BTI (1 << 0) > +#define ARM64_ELF_INTERP_BTI (1 << 0) > +#define ARM64_ELF_EXEC_BTI (1 << 1) > > #define INIT_ARCH_ELF_STATE { \ > .flags = 0, \ > @@ -274,9 +275,14 @@ static inline int arch_parse_elf_property(u32 type, const void *data, > if (datasz != sizeof(*p)) > return -ENOEXEC; > > - if (system_supports_bti() && has_interp == is_interp && > - (*p & GNU_PROPERTY_AARCH64_FEATURE_1_BTI)) > - arch->flags |= ARM64_ELF_BTI; > + if (system_supports_bti() && > + (*p & GNU_PROPERTY_AARCH64_FEATURE_1_BTI)) { > + if (is_interp) { > + arch->flags |= ARM64_ELF_INTERP_BTI; > + } else { > + arch->flags |= ARM64_ELF_EXEC_BTI; > + } Nit: surplus curlies? (coding-style.rst does actually say to drop them when all branches of an if are single-statement one-liners -- I had presumed I was just being pedantic...) > + } > } > > return 0; > diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c > index b4bb67f17a2c..f7fff4a4c99f 100644 > --- a/arch/arm64/kernel/process.c > +++ b/arch/arm64/kernel/process.c > @@ -744,19 +744,13 @@ asmlinkage void __sched arm64_preempt_schedule_irq(void) > int arch_elf_adjust_prot(int prot, const struct arch_elf_state *state, > bool has_interp, bool is_interp) > { > - /* > - * For dynamically linked executables the interpreter is > - * responsible for setting PROT_BTI on everything except > - * itself. > - */ > - if (is_interp != has_interp) > - return prot; > + if (prot & PROT_EXEC) { > + if (state->flags & ARM64_ELF_INTERP_BTI && is_interp) > + prot |= PROT_BTI; > > - if (!(state->flags & ARM64_ELF_BTI)) > - return prot; > - > - if (prot & PROT_EXEC) > - prot |= PROT_BTI; > + if (state->flags & ARM64_ELF_EXEC_BTI && !is_interp) > + prot |= PROT_BTI; > + } Is it worth adding () around the bitwise-& expressions? I'm always a little uneasy about the operator precedence of binary &, although without looking it up I think you're correct. Also, due to symmetry between arch_elf_adjust_prot() and arch_parse_elf_properties() here, could we have something like static inline int arm64_elf_bti_flag(bool is_interp) { if (is_interp) return ARM64_ELF_INTERP_BTI; else return ARM64_ELF_EXEC_BTI; } and then have code like if (state->flags & arm64_elf_bti_flag(is_interp)) prot |= PROT_BTI; here (with analogous code in arch_elf_adjust_prot()). Feel free to adopt if this appeals to you, otherwise I'm also fine with your version.) Either way, these comments are all pretty much cosmetic, and my Reviewed-by stands. Cheers ---Dave
On Wed, Jun 09, 2021 at 04:17:13PM +0100, Dave Martin wrote: > On Fri, Jun 04, 2021 at 12:24:49PM +0100, Mark Brown wrote: > > - if (system_supports_bti() && has_interp == is_interp && > > - (*p & GNU_PROPERTY_AARCH64_FEATURE_1_BTI)) > > - arch->flags |= ARM64_ELF_BTI; > > + if (system_supports_bti() && > > + (*p & GNU_PROPERTY_AARCH64_FEATURE_1_BTI)) { > > + if (is_interp) { > > + arch->flags |= ARM64_ELF_INTERP_BTI; > > + } else { > > + arch->flags |= ARM64_ELF_EXEC_BTI; > > + } > Nit: surplus curlies? (coding-style.rst does actually say to drop them > when all branches of an if are single-statement one-liners -- I had > presumed I was just being pedantic...) I really think this hurts readability with the nested if inside another if with a multi-line condition. > > - if (prot & PROT_EXEC) > > - prot |= PROT_BTI; > > + if (state->flags & ARM64_ELF_EXEC_BTI && !is_interp) > > + prot |= PROT_BTI; > > + } > Is it worth adding () around the bitwise-& expressions? I'm always a > little uneasy about the operator precedence of binary &, although > without looking it up I think you're correct. Sure. I'm fairly sure the compiler would've complained about this case if it were ambiguous, I'm vaguely surprised it didn't already. > Feel free to adopt if this appeals to you, otherwise I'm also fine with > your version.) I'll see what I think when I get back to looking at this properly.
On Thu, Jun 10, 2021 at 02:19:05PM +0100, Mark Brown wrote: > On Wed, Jun 09, 2021 at 04:17:13PM +0100, Dave Martin wrote: > > On Fri, Jun 04, 2021 at 12:24:49PM +0100, Mark Brown wrote: > > > > - if (system_supports_bti() && has_interp == is_interp && > > > - (*p & GNU_PROPERTY_AARCH64_FEATURE_1_BTI)) > > > - arch->flags |= ARM64_ELF_BTI; > > > + if (system_supports_bti() && > > > + (*p & GNU_PROPERTY_AARCH64_FEATURE_1_BTI)) { > > > + if (is_interp) { > > > + arch->flags |= ARM64_ELF_INTERP_BTI; > > > + } else { > > > + arch->flags |= ARM64_ELF_EXEC_BTI; > > > + } > > > Nit: surplus curlies? (coding-style.rst does actually say to drop them > > when all branches of an if are single-statement one-liners -- I had > > presumed I was just being pedantic...) > > I really think this hurts readability with the nested if inside > another if with a multi-line condition. So long as there is a reason rather than it being purely an accident of editing, that's fine. (Though if the nested if can be flattened so that this becomes a non- issue, that's good too :) > > > - if (prot & PROT_EXEC) > > > - prot |= PROT_BTI; > > > + if (state->flags & ARM64_ELF_EXEC_BTI && !is_interp) > > > + prot |= PROT_BTI; > > > + } > > > Is it worth adding () around the bitwise-& expressions? I'm always a > > little uneasy about the operator precedence of binary &, although > > without looking it up I think you're correct. > > Sure. I'm fairly sure the compiler would've complained about > this case if it were ambiguous, I'm vaguely surprised it didn't > already. I was vaguely surprised too -- though I didn't try to compile this myself yet. Anyway, not a huge deal. Adding a helper to generate the appropriate mask would make this issue go away in any case, but so long as you're confident this is being evaluated as intended I can take your word for it. > > Feel free to adopt if this appeals to you, otherwise I'm also fine with > > your version.) > > I'll see what I think when I get back to looking at this > properly. Ack -- again, this was just a suggestion. I can also live with your original code if you ultimately decide to stick with that. Cheers ---Dave
diff --git a/arch/arm64/include/asm/elf.h b/arch/arm64/include/asm/elf.h index a488a1329b16..9f86dbce2680 100644 --- a/arch/arm64/include/asm/elf.h +++ b/arch/arm64/include/asm/elf.h @@ -253,7 +253,8 @@ struct arch_elf_state { int flags; }; -#define ARM64_ELF_BTI (1 << 0) +#define ARM64_ELF_INTERP_BTI (1 << 0) +#define ARM64_ELF_EXEC_BTI (1 << 1) #define INIT_ARCH_ELF_STATE { \ .flags = 0, \ @@ -274,9 +275,14 @@ static inline int arch_parse_elf_property(u32 type, const void *data, if (datasz != sizeof(*p)) return -ENOEXEC; - if (system_supports_bti() && has_interp == is_interp && - (*p & GNU_PROPERTY_AARCH64_FEATURE_1_BTI)) - arch->flags |= ARM64_ELF_BTI; + if (system_supports_bti() && + (*p & GNU_PROPERTY_AARCH64_FEATURE_1_BTI)) { + if (is_interp) { + arch->flags |= ARM64_ELF_INTERP_BTI; + } else { + arch->flags |= ARM64_ELF_EXEC_BTI; + } + } } return 0; diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c index b4bb67f17a2c..f7fff4a4c99f 100644 --- a/arch/arm64/kernel/process.c +++ b/arch/arm64/kernel/process.c @@ -744,19 +744,13 @@ asmlinkage void __sched arm64_preempt_schedule_irq(void) int arch_elf_adjust_prot(int prot, const struct arch_elf_state *state, bool has_interp, bool is_interp) { - /* - * For dynamically linked executables the interpreter is - * responsible for setting PROT_BTI on everything except - * itself. - */ - if (is_interp != has_interp) - return prot; + if (prot & PROT_EXEC) { + if (state->flags & ARM64_ELF_INTERP_BTI && is_interp) + prot |= PROT_BTI; - if (!(state->flags & ARM64_ELF_BTI)) - return prot; - - if (prot & PROT_EXEC) - prot |= PROT_BTI; + if (state->flags & ARM64_ELF_EXEC_BTI && !is_interp) + prot |= PROT_BTI; + } return prot; }