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Date: Thu, 2 Feb 2023 20:43:04 +0000
From: Kees Cook <keescook@...omium.org>
To: Sami Tolvanen <samitolvanen@...gle.com>
Cc: Nick Desaulniers <ndesaulniers@...gle.com>,
Ard Biesheuvel <ardb@...nel.org>,
John Stultz <jstultz@...gle.com>,
Yongqin Liu <yongqin.liu@...aro.org>,
Vlastimil Babka <vbabka@...e.cz>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Rasmus Villemoes <rasmus.villemoes@...vas.dk>,
Thomas Gleixner <tglx@...utronix.de>,
Jason Gunthorpe <jgg@...pe.ca>, Nishanth Menon <nm@...com>,
Michael Kelley <mikelley@...rosoft.com>,
Dan Williams <dan.j.williams@...el.com>,
Won Chung <wonchung@...gle.com>,
David Gow <davidgow@...gle.com>,
Christoph Lameter <cl@...ux.com>,
Pekka Enberg <penberg@...nel.org>,
David Rientjes <rientjes@...gle.com>,
Joonsoo Kim <iamjoonsoo.kim@....com>,
Roman Gushchin <roman.gushchin@...ux.dev>,
Hyeonggon Yoo <42.hyeyoo@...il.com>,
Guenter Roeck <linux@...ck-us.net>,
Andy Shevchenko <andriy.shevchenko@...el.com>,
Paolo Abeni <pabeni@...hat.com>,
Geert Uytterhoeven <geert@...ux-m68k.org>,
Nathan Chancellor <nathan@...nel.org>,
Tom Rix <trix@...hat.com>, linux-kernel@...r.kernel.org,
linux-mm@...ck.org, linux-hardening@...r.kernel.org,
llvm@...ts.linux.dev, Sumit Semwal <sumit.semwal@...aro.org>
Subject: Re: [PATCH 5/6] driver core: Add __alloc_size hint to devm allocators
On Thu, Feb 02, 2023 at 12:11:47PM -0800, Sami Tolvanen wrote:
> On Thu, Feb 2, 2023 at 11:53 AM Kees Cook <keescook@...omium.org> wrote:
> >
> > On Thu, Feb 02, 2023 at 11:49:42AM -0800, Sami Tolvanen wrote:
> > > A quick look at Clang's source code suggests that Intrinsic::ubsantrap
> > > already accepts the handler ID (from the SanitizerHandler enum) as an
> > > argument and the arm64 LLVM back-end appears to encode the value as an
> > > immediate for the brk instruction. I didn't confirm that this actually
> > > works, but perhaps we just need to teach the kernel about the possible
> > > values?
> >
> > Oh excellent. Yeah, if that's all that's needed here that would be
> > great. What are the values?
>
> The arm64 brk immediate encoding seems to be "ubsantrap arg | 'U' << 8":
>
> https://github.com/llvm/llvm-project/blob/main/llvm/lib/Target/AArch64/AArch64InstrInfo.td#L7571
>
> The argument values come from the SanitizerHandler enum, which is
> populated from this list:
>
> https://github.com/llvm/llvm-project/blob/main/clang/lib/CodeGen/CodeGenFunction.h#L113
>
> Therefore, according to the tests, for ubsantrap(12) we'll get brk
> #0x550c, for example:
>
> https://github.com/llvm/llvm-project/blob/main/llvm/test/CodeGen/AArch64/ubsantrap.ll
So the absolute minimal handler would look like this:
diff --git a/arch/arm64/include/asm/brk-imm.h b/arch/arm64/include/asm/brk-imm.h
index 6e000113e508..3f0f0d03268b 100644
--- a/arch/arm64/include/asm/brk-imm.h
+++ b/arch/arm64/include/asm/brk-imm.h
@@ -28,6 +28,8 @@
#define BUG_BRK_IMM 0x800
#define KASAN_BRK_IMM 0x900
#define KASAN_BRK_MASK 0x0ff
+#define UBSAN_BRK_IMM 0x5500
+#define UBSAN_BRK_MASK 0x00ff
#define CFI_BRK_IMM_TARGET GENMASK(4, 0)
#define CFI_BRK_IMM_TYPE GENMASK(9, 5)
diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c
index 4c0caa589e12..36b917d8fa5f 100644
--- a/arch/arm64/kernel/traps.c
+++ b/arch/arm64/kernel/traps.c
@@ -1074,6 +1074,18 @@ static struct break_hook kasan_break_hook = {
};
#endif
+#ifdef CONFIG_UBSAN_TRAP
+static int ubsan_handler(struct pt_regs *regs, unsigned long esr)
+{
+ die("Oops - UBSAN", regs, esr);
+}
+
+static struct break_hook ubsan_break_hook = {
+ .fn = ubsan_handler,
+ .imm = UBSAN_BRK_IMM,
+ .mask = UBSAN_BRK_MASK,
+};
+#endif
#define esr_comment(esr) ((esr) & ESR_ELx_BRK64_ISS_COMMENT_MASK)
@@ -1091,6 +1103,10 @@ int __init early_brk64(unsigned long addr, unsigned long esr,
#ifdef CONFIG_KASAN_SW_TAGS
if ((esr_comment(esr) & ~KASAN_BRK_MASK) == KASAN_BRK_IMM)
return kasan_handler(regs, esr) != DBG_HOOK_HANDLED;
+#endif
+#ifdef CONFIG_UBSAN_TRAP
+ if ((esr_comment(esr) & ~UBSAN_BRK_MASK) == UBSAN_BRK_IMM)
+ return ubsan_handler(regs, esr) != DBG_HOOK_HANDLED;
#endif
return bug_handler(regs, esr) != DBG_HOOK_HANDLED;
}
@@ -1104,6 +1120,9 @@ void __init trap_init(void)
register_kernel_break_hook(&fault_break_hook);
#ifdef CONFIG_KASAN_SW_TAGS
register_kernel_break_hook(&kasan_break_hook);
+#endif
+#ifdef CONFIG_UBSAN_TRAP
+ register_kernel_break_hook(&ubsan_break_hook);
#endif
debug_traps_init();
}
But we could expand ubsan_handler() to extract the SanitizerHandler enum
value and report which UBSAN check was hit...
--
Kees Cook
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