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selftests/x86/sigreturn/32: Invalidate DS and ES when abusing the kernel

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If the kernel accidentally uses DS or ES while the user values are
loaded, it will work fine for sane userspace.  In the interest of
simulating maximally insane userspace, make sigreturn_32 zero out DS
and ES for the nasty parts so that inadvertent use of these segments
will crash.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: stable@kernel.org
This commit is contained in:
Andy Lutomirski 2019-11-20 11:58:32 -08:00 committed by Peter Zijlstra
parent 8caa016bfc
commit 4d2fa82d98
1 changed files with 13 additions and 0 deletions
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13
tools/testing/selftests/x86/sigreturn.c
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@ -451,6 +451,19 @@ static void sigusr1(int sig, siginfo_t *info, void *ctx_void)
ctx->uc_mcontext.gregs[REG_SP] = (unsigned long)0x8badf00d5aadc0deULL;
ctx->uc_mcontext.gregs[REG_CX] = 0;
#ifdef __i386__
/*
* Make sure the kernel doesn't inadvertently use DS or ES-relative
* accesses in a region where user DS or ES is loaded.
*
* Skip this for 64-bit builds because long mode doesn't care about
* DS and ES and skipping it increases test coverage a little bit,
* since 64-bit kernels can still run the 32-bit build.
*/
ctx->uc_mcontext.gregs[REG_DS] = 0;
ctx->uc_mcontext.gregs[REG_ES] = 0;
#endif
memcpy(&requested_regs, &ctx->uc_mcontext.gregs, sizeof(gregset_t));
requested_regs[REG_CX] = *ssptr(ctx); /* The asm code does this. */